diff --git a/dwds/CHANGELOG.md b/dwds/CHANGELOG.md
index bc0cdde6b..fe53aa6c2 100644
--- a/dwds/CHANGELOG.md
+++ b/dwds/CHANGELOG.md
@@ -6,6 +6,7 @@
 - Fix a bug where evaluation would fail with more than one parameter in
   the scope.
 - Remove showing uncaptured values from the stack during evaluation.
+- Refactor code to break most circular dependencies between files.
 
 **Breaking changes**
 - Remove no longer used `ExpressionCompilerService.handler`.
diff --git a/dwds/lib/src/debugging/classes.dart b/dwds/lib/src/debugging/classes.dart
index 112ad8994..a2c8ae927 100644
--- a/dwds/lib/src/debugging/classes.dart
+++ b/dwds/lib/src/debugging/classes.dart
@@ -11,30 +11,15 @@ import '../../src/services/chrome_debug_exception.dart';
 import '../loaders/strategy.dart';
 import '../utilities/domain.dart';
 import '../utilities/shared.dart';
-import 'inspector.dart';
 import 'metadata/class.dart';
 
-/// A hard-coded ClassRef for the Closure class.
-final classRefForClosure = classRefFor('dart:core', 'Closure');
-
-/// A hard-coded ClassRef for the String class.
-final classRefForString = classRefFor('dart:core', InstanceKind.kString);
-
-/// A hard-coded ClassRef for a (non-existent) class called Unknown.
-final classRefForUnknown = classRefFor('dart:core', 'Unknown');
-
-/// Returns a [ClassRef] for the provided library ID and class name.
-ClassRef classRefFor(String libraryId, String name) => ClassRef(
-    id: 'classes|$libraryId|$name',
-    name: name,
-    library: LibraryRef(id: libraryId, name: libraryId, uri: libraryId));
-
 /// Keeps track of Dart classes available in the running application.
 class ClassHelper extends Domain {
   /// Map of class ID to [Class].
   final _classes = <String, Class>{};
 
-  ClassHelper(AppInspector Function() provider) : super(provider) {
+  ClassHelper(AppInspectorInterface appInspector) {
+    inspector = appInspector;
     final staticClasses = [
       classRefForClosure,
       classRefForString,
@@ -67,7 +52,7 @@ class ClassHelper extends Domain {
     if (libraryId == 'null') {
       throw UnsupportedError('unknown library: $libraryId');
     }
-    final libraryRef = await inspector.libraryHelper.libraryRefFor(libraryId);
+    final libraryRef = await inspector.libraryRefFor(libraryId);
     if (libraryRef == null) {
       throw Exception('Could not find library: $libraryId');
     }
diff --git a/dwds/lib/src/debugging/debugger.dart b/dwds/lib/src/debugging/debugger.dart
index 85bb1eb14..6b91e5e1c 100644
--- a/dwds/lib/src/debugging/debugger.dart
+++ b/dwds/lib/src/debugging/debugger.dart
@@ -15,7 +15,6 @@ import 'package:webkit_inspection_protocol/webkit_inspection_protocol.dart'
     hide StackTrace;
 
 import '../loaders/strategy.dart';
-import '../services/chrome_proxy_service.dart';
 import '../services/chrome_debug_exception.dart';
 import '../utilities/conversions.dart';
 import '../utilities/dart_uri.dart';
@@ -28,6 +27,10 @@ import 'location.dart';
 import 'remote_debugger.dart';
 import 'skip_list.dart';
 
+/// Adds [event] to the stream with [streamId] if there is anybody listening
+/// on that stream.
+typedef StreamNotify = void Function(String streamId, Event event);
+
 /// Converts from ExceptionPauseMode strings to [PauseState] enums.
 ///
 /// Values defined in:
@@ -51,16 +54,13 @@ class Debugger extends Domain {
   Debugger._(
     this._remoteDebugger,
     this._streamNotify,
-    AppInspectorProvider provider,
     this._locations,
     this._skipLists,
     this._root,
-  )   : _breakpoints = _Breakpoints(
+  ) : _breakpoints = _Breakpoints(
             locations: _locations,
-            provider: provider,
             remoteDebugger: _remoteDebugger,
-            root: _root),
-        super(provider);
+            root: _root);
 
   /// The breakpoints we have set so far, indexable by either
   /// Dart or JS ID.
@@ -86,6 +86,11 @@ class Debugger extends Domain {
 
   bool _isStepping = false;
 
+  void updateInspector(AppInspectorInterface appInspector) {
+    inspector = appInspector;
+    _breakpoints.inspector = appInspector;
+  }
+
   Future<Success> pause() async {
     _isStepping = false;
     final result = await _remoteDebugger.pause();
@@ -93,8 +98,7 @@ class Debugger extends Domain {
     return Success();
   }
 
-  Future<Success> setExceptionPauseMode(String isolateId, String mode) async {
-    checkIsolate('setExceptionPauseMode', isolateId);
+  Future<Success> setExceptionPauseMode(String mode) async {
     mode = mode?.toLowerCase();
     if (!_pauseModePauseStates.containsKey(mode)) {
       throwInvalidParam('setExceptionPauseMode', 'Unsupported mode: $mode');
@@ -117,9 +121,7 @@ class Debugger extends Domain {
   ///
   /// Note that stepping will automatically continue until Chrome is paused at
   /// a location for which we have source information.
-  Future<Success> resume(String isolateId,
-      {String step, int frameIndex}) async {
-    checkIsolate('resume', isolateId);
+  Future<Success> resume({String step, int frameIndex}) async {
     if (frameIndex != null) {
       throw ArgumentError('FrameIndex is currently unsupported.');
     }
@@ -152,9 +154,7 @@ class Debugger extends Domain {
   /// Returns null if the debugger is not paused.
   ///
   /// The returned stack will contain up to [limit] frames if provided.
-  Future<Stack> getStack(String isolateId, {int limit}) async {
-    checkIsolate('getStack', isolateId);
-
+  Future<Stack> getStack({int limit}) async {
     if (stackComputer == null) {
       throw RPCError('getStack', RPCError.kInternalError,
           'Cannot compute stack when application is not paused');
@@ -170,7 +170,6 @@ class Debugger extends Domain {
   static Future<Debugger> create(
     RemoteDebugger remoteDebugger,
     StreamNotify streamNotify,
-    AppInspectorProvider appInspectorProvider,
     Locations locations,
     SkipLists skipLists,
     String root,
@@ -178,7 +177,6 @@ class Debugger extends Domain {
     final debugger = Debugger._(
       remoteDebugger,
       streamNotify,
-      appInspectorProvider,
       locations,
       skipLists,
       root,
@@ -224,13 +222,11 @@ class Debugger extends Domain {
   ///
   /// Note that line and column are Dart source locations and are one-based.
   Future<Breakpoint> addBreakpoint(
-    String isolateId,
     String scriptId,
     int line, {
     int column,
   }) async {
     column ??= 0;
-    checkIsolate('addBreakpoint', isolateId);
     final breakpoint = await _breakpoints.add(scriptId, line, column);
     _notifyBreakpoint(breakpoint);
     return breakpoint;
@@ -264,9 +260,7 @@ class Debugger extends Domain {
     // Disabled breakpoints were actually removed from Chrome so simply add
     // them back.
     for (var breakpoint in disabledBreakpoints) {
-      await addBreakpoint(
-          inspector.isolate.id,
-          (await _updatedScriptRefFor(breakpoint)).id,
+      await addBreakpoint((await _updatedScriptRefFor(breakpoint)).id,
           _lineNumberFor(breakpoint),
           column: _columnNumberFor(breakpoint));
     }
@@ -283,9 +277,7 @@ class Debugger extends Domain {
   }
 
   /// Remove a Dart breakpoint.
-  Future<Success> removeBreakpoint(
-      String isolateId, String breakpointId) async {
-    checkIsolate('removeBreakpoint', isolateId);
+  Future<Success> removeBreakpoint(String breakpointId) async {
     if (!_breakpoints._bpByDartId.containsKey(breakpointId)) {
       throwInvalidParam(
           'removeBreakpoint', 'invalid breakpoint id $breakpointId');
@@ -361,8 +353,7 @@ class Debugger extends Domain {
   Future<BoundVariable> _boundVariable(Property property) async {
     // We return one level of properties from this object. Sub-properties are
     // another round trip.
-    final instanceRef =
-        await inspector.instanceHelper.instanceRefFor(property.value);
+    final instanceRef = await inspector.instanceRefFor(property.value);
     // Skip null instance refs, which we get for weird objects, e.g.
     // properties that are getter/setter pairs.
     // TODO(alanknight): Handle these properly.
@@ -552,7 +543,7 @@ class Debugger extends Domain {
         if (map['type'] == 'object') {
           // The className here is generally 'DartError'.
           final obj = RemoteObject(map);
-          exception = await inspector.instanceHelper.instanceRefFor(obj);
+          exception = await inspector.instanceRefFor(obj);
 
           // TODO: The exception object generally doesn't get converted to a
           // Dart object (and instead has a classRef name of 'NativeJavaScriptObject').
@@ -561,8 +552,7 @@ class Debugger extends Domain {
               // Create a string exception object.
               final description =
                   await inspector.mapExceptionStackTrace(obj.description);
-              exception =
-                  await inspector.instanceHelper.instanceRefFor(description);
+              exception = await inspector.instanceRefFor(description);
             } else {
               exception = null;
             }
@@ -671,21 +661,6 @@ class Debugger extends Domain {
     logger.severe('Target crashed!');
   }
 
-  /// Evaluate [expression] by calling Chrome's Runtime.evaluate
-  Future<RemoteObject> evaluate(String expression) async {
-    try {
-      return await _remoteDebugger.evaluate(expression);
-    } on ExceptionDetails catch (e) {
-      throw ChromeDebugException(
-        e.json,
-        evalContents: expression,
-        additionalDetails: {
-          'Dart expression': expression,
-        },
-      );
-    }
-  }
-
   WipCallFrame jsFrameForIndex(int frameIndex) {
     if (stackComputer == null) {
       throw RPCError('evaluateInFrame', 106,
@@ -766,10 +741,9 @@ class _Breakpoints extends Domain {
 
   _Breakpoints({
     @required this.locations,
-    @required AppInspectorProvider provider,
     @required this.remoteDebugger,
     @required this.root,
-  }) : super(provider);
+  });
 
   Future<Breakpoint> _createBreakpoint(
       String id, String scriptId, int line, int column) async {
diff --git a/dwds/lib/src/debugging/inspector.dart b/dwds/lib/src/debugging/inspector.dart
index a2b737d06..67c303d86 100644
--- a/dwds/lib/src/debugging/inspector.dart
+++ b/dwds/lib/src/debugging/inspector.dart
@@ -10,8 +10,6 @@ import 'package:vm_service/vm_service.dart';
 import 'package:webkit_inspection_protocol/webkit_inspection_protocol.dart';
 
 import '../connections/app_connection.dart';
-import '../debugging/location.dart';
-import '../debugging/remote_debugger.dart';
 import '../loaders/strategy.dart';
 import '../readers/asset_reader.dart';
 import '../utilities/conversions.dart';
@@ -24,13 +22,15 @@ import 'debugger.dart';
 import 'execution_context.dart';
 import 'instance.dart';
 import 'libraries.dart';
+import 'location.dart';
+import 'remote_debugger.dart';
 
 /// An inspector for a running Dart application contained in the
 /// [WipConnection].
 ///
 /// Provides information about currently loaded scripts and objects and support
 /// for eval.
-class AppInspector extends Domain {
+class AppInspector implements AppInspectorInterface {
   final _scriptCacheMemoizer = AsyncMemoizer<List<ScriptRef>>();
 
   Future<List<ScriptRef>> get scriptRefs => _populateScriptCaches();
@@ -49,16 +49,27 @@ class AppInspector extends Domain {
   /// Map of [Library] id to included [ScriptRef]s.
   final _libraryIdToScriptRefs = <String, List<ScriptRef>>{};
 
-  final RemoteDebugger remoteDebugger;
-  final Debugger debugger;
-  final Isolate isolate;
-  final IsolateRef isolateRef;
-  final AppConnection appConnection;
+  @override
+  RemoteDebugger get remoteDebugger => _remoteDebugger;
+  final RemoteDebugger _remoteDebugger;
+
+  @override
+  Isolate get isolate => _isolate;
+  final Isolate _isolate;
+
+  @override
+  IsolateRef get isolateRef => _isolateRef;
+  final IsolateRef _isolateRef;
+
+  @override
+  AppConnection get appConnection => _appConnection;
+  final AppConnection _appConnection;
+
   final ExecutionContext _executionContext;
 
-  final LibraryHelper libraryHelper;
-  final ClassHelper classHelper;
-  final InstanceHelper instanceHelper;
+  LibraryHelper _libraryHelper;
+  ClassHelper _classHelper;
+  InstanceHelper _instanceHelper;
 
   final AssetReader _assetReader;
   final Locations _locations;
@@ -74,28 +85,27 @@ class AppInspector extends Domain {
   static final exceptionMessageRegex = RegExp(r'^.*$', multiLine: true);
 
   AppInspector._(
-    this.appConnection,
-    this.isolate,
-    this.remoteDebugger,
-    this.debugger,
-    this.libraryHelper,
-    this.classHelper,
-    this.instanceHelper,
+    this._appConnection,
+    this._isolate,
+    this._remoteDebugger,
     this._assetReader,
     this._locations,
     this._root,
     this._executionContext,
     this._sdkConfiguration,
-  )   : isolateRef = _toIsolateRef(isolate),
-        super.forInspector();
+  ) : _isolateRef = _toIsolateRef(_isolate);
 
-  /// We are the inspector, so this getter is trivial.
-  @override
-  AppInspector get inspector => this;
+  Future<void> initialize(
+    LibraryHelper libraryHelper,
+    ClassHelper classHelper,
+    InstanceHelper instanceHelper,
+  ) async {
+    _libraryHelper = libraryHelper;
+    _classHelper = classHelper;
+    _instanceHelper = instanceHelper;
 
-  Future<void> _initialize() async {
-    final libraries = await libraryHelper.libraryRefs;
-    isolate.rootLib = await libraryHelper.rootLib;
+    final libraries = await _libraryHelper.libraryRefs;
+    isolate.rootLib = await _libraryHelper.rootLib;
     isolate.libraries.addAll(libraries);
 
     final scripts = await scriptRefs;
@@ -114,7 +124,7 @@ class AppInspector extends Domain {
         isSystemIsolate: isolate.isSystemIsolate,
       );
 
-  static Future<AppInspector> initialize(
+  static Future<AppInspector> create(
     AppConnection appConnection,
     RemoteDebugger remoteDebugger,
     AssetReader assetReader,
@@ -150,30 +160,33 @@ class AppInspector extends Domain {
         isSystemIsolate: false,
         isolateFlags: [])
       ..extensionRPCs = [];
-    AppInspector appInspector;
-    AppInspector provider() => appInspector;
-    final libraryHelper = LibraryHelper(provider);
-    final classHelper = ClassHelper(provider);
-    final instanceHelper = InstanceHelper(provider);
-    appInspector = AppInspector._(
+    final inspector = AppInspector._(
       appConnection,
       isolate,
       remoteDebugger,
-      debugger,
-      libraryHelper,
-      classHelper,
-      instanceHelper,
       assetReader,
       locations,
       root,
       executionContext,
       sdkConfiguration,
     );
-    await appInspector._initialize();
-    return appInspector;
+
+    debugger.updateInspector(inspector);
+
+    final libraryHelper = LibraryHelper(inspector);
+    final classHelper = ClassHelper(inspector);
+    final instanceHelper = InstanceHelper(inspector, debugger);
+
+    await inspector.initialize(
+      libraryHelper,
+      classHelper,
+      instanceHelper,
+    );
+    return inspector;
   }
 
   /// Returns the ID for the execution context or null if not found.
+  @override
   Future<int> get contextId async {
     try {
       return await _executionContext.id;
@@ -184,6 +197,7 @@ class AppInspector extends Domain {
   }
 
   /// Get the value of the field named [fieldName] from [receiver].
+  @override
   Future<RemoteObject> loadField(RemoteObject receiver, String fieldName) {
     final load = '''
         function() {
@@ -195,7 +209,7 @@ class AppInspector extends Domain {
 
   /// Call a method by name on [receiver], with arguments [positionalArgs] and
   /// [namedArgs].
-  Future<RemoteObject> invokeMethod(RemoteObject receiver, String methodName,
+  Future<RemoteObject> _invokeMethod(RemoteObject receiver, String methodName,
       [List<RemoteObject> positionalArgs = const [],
       Map namedArgs = const {}]) async {
     // TODO(alanknight): Support named arguments.
@@ -217,6 +231,7 @@ class AppInspector extends Domain {
   ///
   /// [evalExpression] should be a JS function definition that can accept
   /// [arguments].
+  @override
   Future<RemoteObject> jsCallFunctionOn(RemoteObject receiver,
       String evalExpression, List<RemoteObject> arguments,
       {bool returnByValue = false}) async {
@@ -258,18 +273,19 @@ class AppInspector extends Domain {
   /// invoking a top-level function. The [arguments] are always strings that are
   /// Dart object Ids (which can also be Chrome RemoteObject objectIds that are
   /// for non-Dart JS objects.)
-  Future<RemoteObject> invoke(String isolateId, String targetId,
-      String selector, List<dynamic> arguments) async {
-    checkIsolate('invoke', isolateId);
+  @override
+  Future<RemoteObject> invoke(
+      String targetId, String selector, List<dynamic> arguments) async {
     final remoteArguments =
         arguments.cast<String>().map(remoteObjectFor).toList();
     // We special case the Dart library, where invokeMethod won't work because
     // it's not really a Dart object.
     if (isLibraryId(targetId)) {
-      final library = await getObject(isolateId, targetId) as Library;
+      final library = await getObject(targetId) as Library;
       return await _invokeLibraryFunction(library, selector, remoteArguments);
     } else {
-      return invokeMethod(remoteObjectFor(targetId), selector, remoteArguments);
+      return _invokeMethod(
+          remoteObjectFor(targetId), selector, remoteArguments);
     }
   }
 
@@ -283,6 +299,7 @@ class AppInspector extends Domain {
   }
 
   /// Evaluate [expression] by calling Chrome's Runtime.evaluate.
+  @override
   Future<RemoteObject> jsEvaluate(String expression,
       {bool awaitPromise = false}) async {
     // TODO(alanknight): Support a version with arguments if needed.
@@ -313,35 +330,47 @@ class AppInspector extends Domain {
   }
 
   /// Call [function] with objects referred by [argumentIds] as arguments.
+  @override
   Future<RemoteObject> callFunction(
       String function, Iterable<String> argumentIds) async {
     final arguments = argumentIds.map(remoteObjectFor).toList();
     return _jsCallFunction(function, arguments);
   }
 
-  Future<Library> getLibrary(String isolateId, String objectId) async {
-    if (isolateId != isolate.id) return null;
-    final libraryRef = await libraryHelper.libraryRefFor(objectId);
+  @override
+  Future<InstanceRef> instanceRefFor(Object value) =>
+      _instanceHelper.instanceRefFor(value);
+
+  Future<Instance> instanceFor(Object value) =>
+      _instanceHelper.instanceFor(value);
+
+  @override
+  Future<LibraryRef> libraryRefFor(String objectId) =>
+      _libraryHelper.libraryRefFor(objectId);
+
+  @override
+  Future<Library> getLibrary(String objectId) async {
+    final libraryRef = await libraryRefFor(objectId);
     if (libraryRef == null) return null;
-    return libraryHelper.libraryFor(libraryRef);
+    return _libraryHelper.libraryFor(libraryRef);
   }
 
-  Future<Obj> getObject(String isolateId, String objectId,
-      {int offset, int count}) async {
+  @override
+  Future<Obj> getObject(String objectId, {int offset, int count}) async {
     try {
-      final library = await getLibrary(isolateId, objectId);
+      final library = await getLibrary(objectId);
       if (library != null) {
         return library;
       }
-      final clazz = await classHelper.forObjectId(objectId);
+      final clazz = await _classHelper.forObjectId(objectId);
       if (clazz != null) {
         return clazz;
       }
       final scriptRef = _scriptRefsById[objectId];
       if (scriptRef != null) {
-        return await _getScript(isolateId, scriptRef);
+        return await _getScript(scriptRef);
       }
-      final instance = await instanceHelper
+      final instance = await _instanceHelper
           .instanceFor(remoteObjectFor(objectId), offset: offset, count: count);
       if (instance != null) {
         return instance;
@@ -354,7 +383,7 @@ class AppInspector extends Domain {
         'are supported for getObject');
   }
 
-  Future<Script> _getScript(String isolateId, ScriptRef scriptRef) async {
+  Future<Script> _getScript(ScriptRef scriptRef) async {
     final libraryId = _scriptIdToLibraryId[scriptRef.id];
     final serverPath = DartUri(scriptRef.uri, _root).serverPath;
     final source = await _assetReader.dartSourceContents(serverPath);
@@ -364,15 +393,14 @@ class AppInspector extends Domain {
     }
     return Script(
         uri: scriptRef.uri,
-        library: await libraryHelper.libraryRefFor(libraryId),
+        library: await libraryRefFor(libraryId),
         id: scriptRef.id)
       ..tokenPosTable = await _locations.tokenPosTableFor(serverPath)
       ..source = source;
   }
 
-  Future<MemoryUsage> getMemoryUsage(String isolateId) async {
-    checkIsolate('getMemoryUsage', isolateId);
-
+  @override
+  Future<MemoryUsage> getMemoryUsage() async {
     final response = await remoteDebugger.sendCommand('Runtime.getHeapUsage');
 
     final jsUsage = HeapUsage(response.result);
@@ -384,12 +412,14 @@ class AppInspector extends Domain {
   }
 
   /// Returns the [ScriptRef] for the provided Dart server path [uri].
+  @override
   Future<ScriptRef> scriptRefFor(String uri) async {
     await _populateScriptCaches();
     return _serverPathToScriptRef[uri];
   }
 
   /// Returns the [ScriptRef]s in the library with [libraryId].
+  @override
   Future<List<ScriptRef>> scriptRefsForLibrary(String libraryId) async {
     await _populateScriptCaches();
     return _libraryIdToScriptRefs[libraryId];
@@ -398,8 +428,8 @@ class AppInspector extends Domain {
   /// Return the VM SourceReport for the given parameters.
   ///
   /// Currently this implements the 'PossibleBreakpoints' report kind.
+  @override
   Future<SourceReport> getSourceReport(
-    String isolateId,
     List<String> reports, {
     String scriptId,
     int tokenPos,
@@ -408,8 +438,6 @@ class AppInspector extends Domain {
     bool reportLines,
     List<String> libraryFilters,
   }) {
-    checkIsolate('getSourceReport', isolateId);
-
     if (reports.contains(SourceReportKind.kCoverage)) {
       throwInvalidParam('getSourceReport',
           'Source report kind ${SourceReportKind.kCoverage} not supported');
@@ -425,16 +453,15 @@ class AppInspector extends Domain {
       throwInvalidParam('getSourceReport', 'Unsupported source report kind.');
     }
 
-    return _getPossibleBreakpoints(isolateId, scriptId);
+    return _getPossibleBreakpoints(scriptId);
   }
 
-  Future<SourceReport> _getPossibleBreakpoints(
-      String isolateId, String vmScriptId) async {
+  Future<SourceReport> _getPossibleBreakpoints(String scriptId) async {
     // TODO(devoncarew): Consider adding some caching for this method.
 
-    final scriptRef = scriptWithId(vmScriptId);
+    final scriptRef = scriptWithId(scriptId);
     if (scriptRef == null) {
-      throwInvalidParam('getSourceReport', 'scriptId not found: $vmScriptId');
+      throwInvalidParam('getSourceReport', 'scriptId not found: $scriptId');
     }
 
     final dartUri = DartUri(scriptRef.uri, _root);
@@ -461,8 +488,8 @@ class AppInspector extends Domain {
   }
 
   /// All the scripts in the isolate.
-  Future<ScriptList> getScripts(String isolateId) async {
-    checkIsolate('getScripts', isolateId);
+  @override
+  Future<ScriptList> getScripts() async {
     return ScriptList(scripts: await scriptRefs);
   }
 
@@ -491,7 +518,7 @@ class AppInspector extends Domain {
           ScriptRef(uri: uri, id: createId()),
           for (var part in parts) ScriptRef(uri: part, id: createId())
         ];
-        final libraryRef = await libraryHelper.libraryRefFor(uri);
+        final libraryRef = await _libraryHelper.libraryRefFor(uri);
         _libraryIdToScriptRefs.putIfAbsent(libraryRef.id, () => <ScriptRef>[]);
         for (var scriptRef in scriptRefs) {
           _scriptRefsById[scriptRef.id] = scriptRef;
@@ -506,6 +533,7 @@ class AppInspector extends Domain {
   }
 
   /// Look up the script by id in an isolate.
+  @override
   ScriptRef scriptWithId(String scriptId) => _scriptRefsById[scriptId];
 
   /// Runs an eval on the page to compute all existing registered extensions.
@@ -533,6 +561,7 @@ class AppInspector extends Domain {
 
   /// Convert a JS exception description into a description containing
   /// a Dart stack trace.
+  @override
   Future<String> mapExceptionStackTrace(String description) async {
     RemoteObject mapperResult;
     try {
diff --git a/dwds/lib/src/debugging/instance.dart b/dwds/lib/src/debugging/instance.dart
index 5a6062527..5bd5324f2 100644
--- a/dwds/lib/src/debugging/instance.dart
+++ b/dwds/lib/src/debugging/instance.dart
@@ -14,16 +14,17 @@ import '../utilities/conversions.dart';
 import '../utilities/domain.dart';
 import '../utilities/objects.dart';
 import '../utilities/shared.dart';
-import 'classes.dart';
 import 'debugger.dart';
-import 'inspector.dart';
 import 'metadata/class.dart';
 import 'metadata/function.dart';
 
 /// Contains a set of methods for getting [Instance]s and [InstanceRef]s.
 class InstanceHelper extends Domain {
-  InstanceHelper(AppInspector Function() provider) : super(provider);
+  InstanceHelper(AppInspectorInterface appInspector, this.debugger) {
+    inspector = appInspector;
+  }
 
+  final Debugger debugger;
   static final InstanceRef kNullInstanceRef =
       _primitiveInstanceRef(InstanceKind.kNull, null);
 
@@ -109,11 +110,8 @@ class InstanceHelper extends Domain {
       return _closureInstanceFor(remoteObject);
     }
 
-    final properties = await inspector.debugger.getProperties(
-        remoteObject.objectId,
-        offset: offset,
-        count: count,
-        length: metaData.length);
+    final properties = await debugger.getProperties(remoteObject.objectId,
+        offset: offset, count: count, length: metaData.length);
     if (metaData.isSystemList) {
       return await _listInstanceFor(
           classRef, remoteObject, properties, offset, count);
diff --git a/dwds/lib/src/debugging/libraries.dart b/dwds/lib/src/debugging/libraries.dart
index b028a323b..bc6b1738d 100644
--- a/dwds/lib/src/debugging/libraries.dart
+++ b/dwds/lib/src/debugging/libraries.dart
@@ -9,7 +9,6 @@ import 'package:vm_service/vm_service.dart';
 
 import '../loaders/strategy.dart';
 import '../utilities/domain.dart';
-import 'inspector.dart';
 import 'metadata/class.dart';
 
 /// Keeps track of Dart libraries available in the running application.
@@ -24,7 +23,9 @@ class LibraryHelper extends Domain {
 
   LibraryRef _rootLib;
 
-  LibraryHelper(AppInspector Function() provider) : super(provider);
+  LibraryHelper(AppInspectorInterface appInspector) {
+    inspector = appInspector;
+  }
 
   Future<LibraryRef> get rootLib async {
     if (_rootLib != null) return _rootLib;
diff --git a/dwds/lib/src/debugging/metadata/class.dart b/dwds/lib/src/debugging/metadata/class.dart
index 4af2a8df0..01051996a 100644
--- a/dwds/lib/src/debugging/metadata/class.dart
+++ b/dwds/lib/src/debugging/metadata/class.dart
@@ -7,12 +7,26 @@
 import 'package:vm_service/vm_service.dart';
 import 'package:webkit_inspection_protocol/webkit_inspection_protocol.dart';
 
-import '../../debugging/classes.dart';
 import '../../debugging/inspector.dart';
 import '../../debugging/remote_debugger.dart';
 import '../../loaders/strategy.dart';
 import '../../services/chrome_debug_exception.dart';
 
+/// A hard-coded ClassRef for the Closure class.
+final classRefForClosure = classRefFor('dart:core', 'Closure');
+
+/// A hard-coded ClassRef for the String class.
+final classRefForString = classRefFor('dart:core', InstanceKind.kString);
+
+/// A hard-coded ClassRef for a (non-existent) class called Unknown.
+final classRefForUnknown = classRefFor('dart:core', 'Unknown');
+
+/// Returns a [ClassRef] for the provided library ID and class name.
+ClassRef classRefFor(String libraryId, String name) => ClassRef(
+    id: 'classes|$libraryId|$name',
+    name: name,
+    library: LibraryRef(id: libraryId, name: libraryId, uri: libraryId));
+
 /// Meta data for a remote Dart class in Chrome.
 class ClassMetaData {
   /// The name of the JS constructor for the object.
diff --git a/dwds/lib/src/dwds_vm_client.dart b/dwds/lib/src/dwds_vm_client.dart
index 980e11b30..344f945b7 100644
--- a/dwds/lib/src/dwds_vm_client.dart
+++ b/dwds/lib/src/dwds_vm_client.dart
@@ -209,8 +209,7 @@ Future<Map<String, dynamic>> _hotRestart(
     // Generate run id to hot restart all apps loaded into the tab.
     final runId = const Uuid().v4().toString();
     _logger.info('Issuing \$dartHotRestartDwds request');
-    await chromeProxyService
-        .appInspectorProvider()
+    await chromeProxyService.inspector
         .jsEvaluate('\$dartHotRestartDwds(\'$runId\');', awaitPromise: true);
     _logger.info('\$dartHotRestartDwds request complete.');
   } on WipError catch (exception) {
@@ -235,7 +234,6 @@ Future<Map<String, dynamic>> _hotRestart(
       }
     };
   }
-
   _logger.info('Waiting for Isolate Start event.');
   await stream.firstWhere((event) => event.kind == EventKind.kIsolateStart);
   chromeProxyService.terminatingIsolates = false;
diff --git a/dwds/lib/src/injected/client.js b/dwds/lib/src/injected/client.js
index 62a523f29..8bd1f2b66 100644
--- a/dwds/lib/src/injected/client.js
+++ b/dwds/lib/src/injected/client.js
@@ -25417,7 +25417,7 @@
   };
   A.RequireRestarter__reloadModule_closure0.prototype = {
     call$1(e) {
-      return this.completer.completeError$2(new A.HotReloadFailedException(J.get$message$x(type$.JsError._as(e))), this.stackTrace);
+      this.completer.completeError$2(new A.HotReloadFailedException(J.get$message$x(type$.JsError._as(e))), this.stackTrace);
     },
     $signature: 80
   };
diff --git a/dwds/lib/src/services/chrome_proxy_service.dart b/dwds/lib/src/services/chrome_proxy_service.dart
index b81e4d72e..7142bcba6 100644
--- a/dwds/lib/src/services/chrome_proxy_service.dart
+++ b/dwds/lib/src/services/chrome_proxy_service.dart
@@ -34,15 +34,6 @@ import '../utilities/sdk_configuration.dart';
 import '../utilities/shared.dart';
 import 'expression_evaluator.dart';
 
-/// Adds [event] to the stream with [streamId] if there is anybody listening
-/// on that stream.
-typedef StreamNotify = void Function(String streamId, Event event);
-
-/// Returns the [AppInspector] for the current tab.
-///
-/// This may be null during a hot restart or page refresh.
-typedef AppInspectorProvider = AppInspector Function();
-
 /// A proxy from the chrome debug protocol to the dart vm service protocol.
 class ChromeProxyService implements VmServiceInterface {
   /// Cache of all existing StreamControllers.
@@ -55,12 +46,12 @@ class ChromeProxyService implements VmServiceInterface {
   final VM _vm;
 
   /// Signals when isolate is intialized.
-  Completer<void> _initializedCompleter = Completer<void>();
   Future<void> get isInitialized => _initializedCompleter.future;
+  Completer<void> _initializedCompleter = Completer<void>();
 
   /// Signals when expression compiler is ready to evaluate.
-  Completer<void> _compilerCompleter = Completer<void>();
   Future<void> get isCompilerInitialized => _compilerCompleter.future;
+  Completer<void> _compilerCompleter = Completer<void>();
 
   /// The root at which we're serving.
   final String root;
@@ -68,9 +59,6 @@ class ChromeProxyService implements VmServiceInterface {
   final RemoteDebugger remoteDebugger;
   final ExecutionContext executionContext;
 
-  /// Provides debugger-related functionality.
-  Future<Debugger> get _debugger => _debuggerCompleter.future;
-
   final AssetReader _assetReader;
 
   final Locations _locations;
@@ -79,15 +67,13 @@ class ChromeProxyService implements VmServiceInterface {
 
   final Modules _modules;
 
+  /// Provides debugger-related functionality.
+  Future<Debugger> get debuggerFuture => _debuggerCompleter.future;
   final _debuggerCompleter = Completer<Debugger>();
 
+  AppInspector get inspector => _inspector;
   AppInspector _inspector;
 
-  /// Public only for testing.
-  ///
-  /// Returns the [AppInspector] this service uses.
-  AppInspector appInspectorProvider() => _inspector;
-
   StreamSubscription<ConsoleAPIEvent> _consoleSubscription;
 
   final _disabledBreakpoints = <Breakpoint>{};
@@ -117,12 +103,11 @@ class ChromeProxyService implements VmServiceInterface {
     final debugger = Debugger.create(
       remoteDebugger,
       _streamNotify,
-      appInspectorProvider,
       _locations,
       _skipLists,
       root,
     );
-    _debuggerCompleter.complete(debugger);
+    debugger.then((value) => _debuggerCompleter.complete(value));
   }
 
   static Future<ChromeProxyService> create(
@@ -213,18 +198,18 @@ class ChromeProxyService implements VmServiceInterface {
     }
     // Waiting for the debugger to be ready before initializing the entrypoint.
     //
-    // Note: moving `await _debugger` after the `_initalizeEntryPoint` call
+    // Note: moving `await debugger` after the `_initalizeEntryPoint` call
     // causes `getcwd` system calls to fail. Since that system call is used
     // in first `Uri.base` call in the expression compiler service isolate,
     // the expression compiler service will fail to start.
     // Issue: https://github.com/dart-lang/webdev/issues/1282
-    final debugger = await _debugger;
+    final debugger = await debuggerFuture;
     final entrypoint = appConnection.request.entrypointPath;
     await _initializeEntrypoint(entrypoint);
     final sdkConfiguration = await _sdkConfigurationProvider.configuration;
 
     debugger.notifyPausedAtStart();
-    _inspector = await AppInspector.initialize(
+    _inspector = await AppInspector.create(
       appConnection,
       remoteDebugger,
       _assetReader,
@@ -234,12 +219,14 @@ class ChromeProxyService implements VmServiceInterface {
       executionContext,
       sdkConfiguration,
     );
+    debugger.updateInspector(_inspector);
 
     _expressionEvaluator = _compiler == null
         ? null
         : ExpressionEvaluator(
             entrypoint,
             _inspector,
+            debugger,
             _locations,
             _modules,
             _compiler,
@@ -319,7 +306,7 @@ class ChromeProxyService implements VmServiceInterface {
     if (isolate == null) return;
     _disabledBreakpoints.addAll(isolate.breakpoints);
     for (var breakpoint in isolate.breakpoints.toList()) {
-      await (await _debugger).removeBreakpoint(isolate.id, breakpoint.id);
+      await (await debuggerFuture).removeBreakpoint(breakpoint.id);
     }
   }
 
@@ -327,8 +314,8 @@ class ChromeProxyService implements VmServiceInterface {
   Future<Breakpoint> addBreakpoint(String isolateId, String scriptId, int line,
       {int column}) async {
     await isInitialized;
-    return (await _debugger)
-        .addBreakpoint(isolateId, scriptId, line, column: column);
+    _checkIsolate('addBreakpoint', isolateId);
+    return (await debuggerFuture).addBreakpoint(scriptId, line, column: column);
   }
 
   @override
@@ -341,6 +328,7 @@ class ChromeProxyService implements VmServiceInterface {
       String isolateId, String scriptUri, int line,
       {int column}) async {
     await isInitialized;
+    _checkIsolate('addBreakpointWithScriptUri', isolateId);
     if (Uri.parse(scriptUri).scheme == 'dart') {
       _logger.finest('Cannot set breakpoint at $scriptUri:$line:$column: '
           'breakpoints in dart SDK locations are not supported yet.');
@@ -354,16 +342,15 @@ class ChromeProxyService implements VmServiceInterface {
     }
     final dartUri = DartUri(scriptUri, root);
     final ref = await _inspector.scriptRefFor(dartUri.serverPath);
-    return (await _debugger)
-        .addBreakpoint(isolateId, ref.id, line, column: column);
+    return (await debuggerFuture).addBreakpoint(ref.id, line, column: column);
   }
 
   @override
   Future<Response> callServiceExtension(String method,
       {String isolateId, Map args}) async {
     await isInitialized;
-    // Validate the isolate id is correct, _getIsolate throws if not.
-    if (isolateId != null) _getIsolate(isolateId);
+    isolateId ??= _inspector.isolate.id;
+    _checkIsolate('callServiceExtension', isolateId);
     args ??= <String, String>{};
     final stringArgs = args.map((k, v) => MapEntry(
         k is String ? k : jsonEncode(k), v is String ? v : jsonEncode(v)));
@@ -397,14 +384,6 @@ ${globalLoadStrategy.loadModuleSnippet}("dart_sdk").developer.invokeExtension(
     return _rpcNotSupportedFuture('clearVMTimeline');
   }
 
-  void _validateIsolateId(String isolateId) {
-    final isolate = _inspector?.isolate;
-    if (isolate?.id != isolateId) {
-      throw RPCError('evaluateInFrame', RPCError.kInvalidParams,
-          'Unrecognized isolate id: $isolateId. Supported isolate: ${isolate?.id}');
-    }
-  }
-
   Future<Response> _getEvaluationResult(
       Future<RemoteObject> Function() evaluation, String expression) async {
     try {
@@ -426,7 +405,7 @@ ${globalLoadStrategy.loadModuleSnippet}("dart_sdk").developer.invokeExtension(
           id: createId(),
         );
       }
-      return _inspector?.instanceHelper?.instanceRefFor(result);
+      return _inspector?.instanceRefFor(result);
     } on RPCError catch (_) {
       rethrow;
     } catch (e, s) {
@@ -454,9 +433,9 @@ ${globalLoadStrategy.loadModuleSnippet}("dart_sdk").developer.invokeExtension(
       await isInitialized;
       if (_expressionEvaluator != null) {
         await isCompilerInitialized;
-        _validateIsolateId(isolateId);
+        _checkIsolate('evaluate', isolateId);
 
-        final library = await _inspector?.getLibrary(isolateId, targetId);
+        final library = await _inspector?.getLibrary(targetId);
         return await _getEvaluationResult(
             () => _expressionEvaluator.evaluateExpression(
                 isolateId, library.uri, expression, scope),
@@ -477,7 +456,7 @@ ${globalLoadStrategy.loadModuleSnippet}("dart_sdk").developer.invokeExtension(
       await isInitialized;
       if (_expressionEvaluator != null) {
         await isCompilerInitialized;
-        _validateIsolateId(isolateId);
+        _checkIsolate('evaluateInFrame', isolateId);
 
         if (scope != null) {
           // TODO(annagrin): Implement scope support.
@@ -537,6 +516,7 @@ ${globalLoadStrategy.loadModuleSnippet}("dart_sdk").developer.invokeExtension(
   Future<Isolate> getIsolate(String isolateId) async {
     return captureElapsedTime(() async {
       await isInitialized;
+      _checkIsolate('getIsolate', isolateId);
       return _getIsolate(isolateId);
     }, (result) => DwdsEvent.getIsolate());
   }
@@ -544,22 +524,24 @@ ${globalLoadStrategy.loadModuleSnippet}("dart_sdk").developer.invokeExtension(
   @override
   Future<MemoryUsage> getMemoryUsage(String isolateId) async {
     await isInitialized;
-    return _inspector.getMemoryUsage(isolateId);
+    _checkIsolate('getMemoryUsage', isolateId);
+    return _inspector.getMemoryUsage();
   }
 
   @override
   Future<Obj> getObject(String isolateId, String objectId,
       {int offset, int count}) async {
     await isInitialized;
-    return _inspector?.getObject(isolateId, objectId,
-        offset: offset, count: count);
+    _checkIsolate('getObject', isolateId);
+    return _inspector?.getObject(objectId, offset: offset, count: count);
   }
 
   @override
   Future<ScriptList> getScripts(String isolateId) async {
     return await captureElapsedTime(() async {
       await isInitialized;
-      return _inspector?.getScripts(isolateId);
+      _checkIsolate('getScripts', isolateId);
+      return _inspector?.getScripts();
     }, (result) => DwdsEvent.getScripts());
   }
 
@@ -576,8 +558,8 @@ ${globalLoadStrategy.loadModuleSnippet}("dart_sdk").developer.invokeExtension(
   }) async {
     return await captureElapsedTime(() async {
       await isInitialized;
+      _checkIsolate('getSourceReport', isolateId);
       return await _inspector?.getSourceReport(
-        isolateId,
         reports,
         scriptId: scriptId,
         tokenPos: tokenPos,
@@ -597,7 +579,8 @@ ${globalLoadStrategy.loadModuleSnippet}("dart_sdk").developer.invokeExtension(
   @override
   Future<Stack> getStack(String isolateId, {int limit}) async {
     await isInitialized;
-    return (await _debugger).getStack(isolateId, limit: limit);
+    _checkIsolate('getStack', isolateId);
+    return (await debuggerFuture).getStack(limit: limit);
   }
 
   @override
@@ -629,10 +612,10 @@ ${globalLoadStrategy.loadModuleSnippet}("dart_sdk").developer.invokeExtension(
       String isolateId, String targetId, String selector, List argumentIds,
       {bool disableBreakpoints}) async {
     await isInitialized;
+    _checkIsolate('invoke', isolateId);
     // TODO(798) - respect disableBreakpoints.
-    final remote =
-        await _inspector?.invoke(isolateId, targetId, selector, argumentIds);
-    final result = _inspector?.instanceHelper?.instanceRefFor(remote);
+    final remote = await _inspector?.invoke(targetId, selector, argumentIds);
+    final result = _inspector?.instanceRefFor(remote);
     if (result == null) {
       throw ChromeDebugException(
           {'text': 'null result from invoke of $selector'});
@@ -687,7 +670,8 @@ ${globalLoadStrategy.loadModuleSnippet}("dart_sdk").developer.invokeExtension(
   @override
   Future<Success> pause(String isolateId) async {
     await isInitialized;
-    return (await _debugger).pause();
+    _checkIsolate('pause', isolateId);
+    return (await debuggerFuture).pause();
   }
 
   // Note: Ignore the optional local parameter, it is there to keep the method
@@ -696,12 +680,14 @@ ${globalLoadStrategy.loadModuleSnippet}("dart_sdk").developer.invokeExtension(
   Future<UriList> lookupResolvedPackageUris(String isolateId, List<String> uris,
       {bool local}) async {
     await isInitialized;
+    _checkIsolate('lookupResolvedPackageUris', isolateId);
     return UriList(uris: uris.map(DartUri.toResolvedUri).toList());
   }
 
   @override
   Future<UriList> lookupPackageUris(String isolateId, List<String> uris) async {
     await isInitialized;
+    _checkIsolate('lookupPackageUris', isolateId);
     return UriList(uris: uris.map(DartUri.toPackageUri).toList());
   }
 
@@ -724,9 +710,10 @@ ${globalLoadStrategy.loadModuleSnippet}("dart_sdk").developer.invokeExtension(
   Future<Success> removeBreakpoint(
       String isolateId, String breakpointId) async {
     await isInitialized;
+    _checkIsolate('removeBreakpoint', isolateId);
     _disabledBreakpoints
         .removeWhere((breakpoint) => breakpoint.id == breakpointId);
-    return (await _debugger).removeBreakpoint(isolateId, breakpointId);
+    return (await debuggerFuture).removeBreakpoint(breakpointId);
   }
 
   @override
@@ -736,8 +723,9 @@ ${globalLoadStrategy.loadModuleSnippet}("dart_sdk").developer.invokeExtension(
     if (_inspector.appConnection.isStarted) {
       return captureElapsedTime(() async {
         await isInitialized;
-        return await (await _debugger)
-            .resume(isolateId, step: step, frameIndex: frameIndex);
+        _checkIsolate('resume', isolateId);
+        return await (await debuggerFuture)
+            .resume(step: step, frameIndex: frameIndex);
       }, (result) => DwdsEvent.resume(step));
     } else {
       _inspector.appConnection.runMain();
@@ -756,7 +744,8 @@ ${globalLoadStrategy.loadModuleSnippet}("dart_sdk").developer.invokeExtension(
   @override
   Future<Success> setExceptionPauseMode(String isolateId, String mode) async {
     await isInitialized;
-    return (await _debugger).setExceptionPauseMode(isolateId, mode);
+    _checkIsolate('setExceptionPauseMode', isolateId);
+    return (await debuggerFuture).setExceptionPauseMode(mode);
   }
 
   @override
@@ -773,6 +762,7 @@ ${globalLoadStrategy.loadModuleSnippet}("dart_sdk").developer.invokeExtension(
   @override
   Future<Success> setName(String isolateId, String name) async {
     await isInitialized;
+    _checkIsolate('setName', isolateId);
     final isolate = _getIsolate(isolateId);
     isolate.name = name;
     return Success();
@@ -940,8 +930,7 @@ ${globalLoadStrategy.loadModuleSnippet}("dart_sdk").developer.invokeExtension(
           // All inspected objects should be real objects.
           if (event.args[1].type != 'object') break;
 
-          final inspectee =
-              await _inspector.instanceHelper.instanceRefFor(event.args[1]);
+          final inspectee = await _inspector.instanceRefFor(event.args[1]);
           _streamNotify(
               EventStreams.kDebug,
               Event(
@@ -1049,7 +1038,7 @@ ${globalLoadStrategy.loadModuleSnippet}("dart_sdk").developer.invokeExtension(
     if (obj == null) {
       return InstanceHelper.kNullInstanceRef;
     } else {
-      return _inspector.instanceHelper.instanceRefFor(obj);
+      return _inspector.instanceRefFor(obj);
     }
   }
 
@@ -1094,6 +1083,28 @@ ${globalLoadStrategy.loadModuleSnippet}("dart_sdk").developer.invokeExtension(
   dynamic noSuchMethod(Invocation invocation) {
     return super.noSuchMethod(invocation);
   }
+
+  /// Validate that isolateId matches the current isolate we're connected to and
+  /// return that isolate.
+  ///
+  /// This is useful to call at the beginning of API methods that are passed an
+  /// isolate id.
+  Isolate _checkIsolate(String methodName, String isolateId) {
+    if (inspector == null) {
+      throw StateError('No inspector set in Domain');
+    }
+    final isolate = _inspector.isolate;
+    if (isolateId != isolate.id) {
+      _throwSentinel(methodName, SentinelKind.kCollected,
+          'Unrecognized isolateId: $isolateId');
+    }
+    return isolate;
+  }
+
+  static void _throwSentinel(String method, String kind, String message) {
+    final data = <String, String>{'kind': kind, 'valueAsString': message};
+    throw SentinelException.parse(method, data);
+  }
 }
 
 /// The `type`s of [ConsoleAPIEvent]s that are treated as `stderr` logs.
diff --git a/dwds/lib/src/services/expression_compiler_service.dart b/dwds/lib/src/services/expression_compiler_service.dart
index 1c86a40f6..f111c3d5a 100644
--- a/dwds/lib/src/services/expression_compiler_service.dart
+++ b/dwds/lib/src/services/expression_compiler_service.dart
@@ -207,8 +207,8 @@ class _Compiler {
 /// ports. It also handles full dill file read requests from the isolate
 /// and redirects them to the asset server.
 ///
-/// Uses [_address] and [_port] to communicate and [_assetHandler] to
-/// redirect asset requests to the asset server.
+/// Uses [_address] and [_port] to communicate and to redirect asset
+/// requests to the asset server.
 ///
 /// Configuration created by [_sdkConfigurationProvider] describes the
 /// locations of SDK files used in expression compilation (summaries,
diff --git a/dwds/lib/src/services/expression_evaluator.dart b/dwds/lib/src/services/expression_evaluator.dart
index 8d86e8300..32e9f4ed7 100644
--- a/dwds/lib/src/services/expression_evaluator.dart
+++ b/dwds/lib/src/services/expression_evaluator.dart
@@ -4,11 +4,12 @@
 
 // @dart = 2.9
 
+import 'package:dwds/src/utilities/domain.dart';
 import 'package:logging/logging.dart';
 import 'package:webkit_inspection_protocol/webkit_inspection_protocol.dart';
 
 import '../debugging/dart_scope.dart';
-import '../debugging/inspector.dart';
+import '../debugging/debugger.dart';
 import '../debugging/location.dart';
 import '../debugging/modules.dart';
 import '../loaders/strategy.dart';
@@ -36,7 +37,8 @@ class ErrorKind {
 /// ExpressionCompilerInterface to compile dart expressions to JavaScript.
 class ExpressionEvaluator {
   final String _entrypoint;
-  final AppInspector _inspector;
+  final AppInspectorInterface _inspector;
+  final Debugger _debugger;
   final Locations _locations;
   final Modules _modules;
   final ExpressionCompiler _compiler;
@@ -53,8 +55,8 @@ class ExpressionEvaluator {
   static final _loadModuleErrorRegex =
       RegExp(r".*Failed to load '.*\.com/(.*\.js).*");
 
-  ExpressionEvaluator(this._entrypoint, this._inspector, this._locations,
-      this._modules, this._compiler);
+  ExpressionEvaluator(this._entrypoint, this._inspector, this._debugger,
+      this._locations, this._modules, this._compiler);
 
   RemoteObject _createError(ErrorKind severity, String message) {
     return RemoteObject(
@@ -141,7 +143,7 @@ class ExpressionEvaluator {
     }
 
     // Get JS scope and current JS location.
-    final jsFrame = _inspector.debugger.jsFrameForIndex(frameIndex);
+    final jsFrame = _debugger.jsFrameForIndex(frameIndex);
     if (jsFrame == null) {
       return _createError(
           ErrorKind.internal,
@@ -203,8 +205,7 @@ class ExpressionEvaluator {
     jsCode = _createTryCatch(jsCode);
 
     // Send JS expression to chrome to evaluate.
-    var result = await _inspector.debugger
-        .evaluateJsOnCallFrameIndex(frameIndex, jsCode);
+    var result = await _debugger.evaluateJsOnCallFrameIndex(frameIndex, jsCode);
     result = await _formatEvaluationError(result);
 
     _logger.finest('Evaluated "$expression" to "$result"');
@@ -276,7 +277,7 @@ class ExpressionEvaluator {
     final scopeChain = filterScopes(frame).reversed;
     for (var scope in scopeChain) {
       final scopeProperties =
-          await _inspector.debugger.getProperties(scope.object.objectId);
+          await _debugger.getProperties(scope.object.objectId);
 
       collectVariables(scope.scope, scopeProperties);
     }
diff --git a/dwds/lib/src/utilities/domain.dart b/dwds/lib/src/utilities/domain.dart
index 9e465dc72..b4df704ce 100644
--- a/dwds/lib/src/utilities/domain.dart
+++ b/dwds/lib/src/utilities/domain.dart
@@ -4,48 +4,111 @@
 
 // @dart = 2.9
 
-import 'package:meta/meta.dart';
 import 'package:vm_service/vm_service.dart';
+import 'package:webkit_inspection_protocol/webkit_inspection_protocol.dart';
 
-import '../debugging/inspector.dart';
-import '../services/chrome_proxy_service.dart';
+import '../connections/app_connection.dart';
+import '../debugging/remote_debugger.dart';
+
+abstract class AppInspectorInterface {
+  /// Connection to the app running in the browser.
+  AppConnection get appConnection;
+
+  /// Remove debugger that supports debugging JS app in the browser.
+  RemoteDebugger get remoteDebugger;
+
+  /// Current running isolate.
+  Isolate get isolate;
+  IsolateRef get isolateRef;
+
+  /// Returns the ID for the execution context or null if not found.
+  Future<int> get contextId;
+
+  /// Calls Chrome's Runtime.callFunctionOn method.
+  ///
+  /// [evalExpression] should be a JS function definition that can accept
+  /// [arguments].
+  Future<RemoteObject> jsCallFunctionOn(RemoteObject receiver,
+      String evalExpression, List<RemoteObject> arguments,
+      {bool returnByValue = false});
+
+  /// Returns the [ScriptRef] for the provided Dart server path [uri].
+  Future<ScriptRef> scriptRefFor(String uri);
+
+  /// Look up the script by id in an isolate.
+  ScriptRef scriptWithId(String scriptId);
+
+  /// Returns the [LibraryRef] for the provided Dart [objectId].
+  Future<LibraryRef> libraryRefFor(String objectId);
+
+  /// Returns the [Library] for the provided Dart [objectId].
+  Future<Library> getLibrary(String objectId);
+
+  /// Returns the [ScriptRef]s in the library with [libraryId].
+  Future<List<ScriptRef>> scriptRefsForLibrary(String libraryId);
+
+  /// Create an InstanceRef for an object, which may be a RemoteObject, or may
+  /// be something returned by value from Chrome, e.g. number, boolean, or
+  /// String.
+  Future<InstanceRef> instanceRefFor(Object value);
+
+  /// Get the value of the field named [fieldName] from [receiver].
+  Future<RemoteObject> loadField(RemoteObject receiver, String fieldName);
+
+  /// Convert a JS exception description into a description containing
+  /// a Dart stack trace.
+  Future<String> mapExceptionStackTrace(String description);
+
+  /// Call [function] with objects referred by [argumentIds] as arguments.
+  Future<RemoteObject> callFunction(
+      String function, Iterable<String> argumentIds);
+
+  /// Invoke the function named [selector] on the object identified by
+  /// [targetId].
+  ///
+  /// The [targetId] can be the URL of a Dart library, in which case this means
+  /// invoking a top-level function. The [arguments] are always strings that are
+  /// Dart object Ids (which can also be Chrome RemoteObject objectIds that are
+  /// for non-Dart JS objects.)
+  Future<RemoteObject> invoke(
+      String targetId, String selector, List<dynamic> arguments);
+
+  /// Evaluate [expression] by calling Chrome's `Runtime.evaluate`.
+  Future<RemoteObject> jsEvaluate(String expression);
+
+  /// Lookup an `object` from some isolate by its [objectId].
+  Future<Obj> getObject(String objectId, {int offset, int count});
+
+  /// All the scripts in the isolate.
+  Future<ScriptList> getScripts();
+
+  /// Return the VM SourceReport for the given parameters.
+  ///
+  /// Currently this implements the 'PossibleBreakpoints' report kind.
+  Future<SourceReport> getSourceReport(
+    List<String> reports, {
+    String scriptId,
+    int tokenPos,
+    int endTokenPos,
+    bool forceCompile,
+    bool reportLines,
+    List<String> libraryFilters,
+  });
+
+  /// Lookup current isolate's memory usage statistics.
+  Future<MemoryUsage> getMemoryUsage();
+}
 
 /// A common superclass to allow implementations of different parts of the
 /// protocol to get access to the inspector and utility functions.
 ///
 /// Subclasses should call the super constructor with the AppInspectorProvider.
 abstract class Domain {
-  final AppInspectorProvider _appInspectorProvider;
-
-  Domain(this._appInspectorProvider);
+  Domain();
 
-  /// A constructor for the AppInspector to call which doesn't set
-  /// [_appInspectorProvider] as it's not used by the AppInspector.
-  Domain.forInspector() : _appInspectorProvider = null;
-
-  AppInspector get inspector => _appInspectorProvider();
+  AppInspectorInterface inspector;
+}
 
-  /// Validate that isolateId matches the current isolate we're connected to and
-  /// return that isolate.
-  ///
-  /// This is useful to call at the beginning of API methods that are passed an
-  /// isolate id.
-  Isolate checkIsolate(String methodName, String isolateId) {
-    if (isolateId != inspector.isolate?.id) {
-      throwSentinel(methodName, SentinelKind.kCollected,
-          'Unrecognized isolateId: $isolateId');
-    }
-    return inspector.isolate;
-  }
-
-  @alwaysThrows
-  void throwInvalidParam(String method, String message) {
-    throw RPCError(method, RPCError.kInvalidParams, message);
-  }
-
-  @alwaysThrows
-  void throwSentinel(String method, String kind, String message) {
-    final data = <String, String>{'kind': kind, 'valueAsString': message};
-    throw SentinelException.parse(method, data);
-  }
+void throwInvalidParam(String method, String message) {
+  throw RPCError(method, RPCError.kInvalidParams, message);
 }
diff --git a/dwds/test/chrome_proxy_service_test.dart b/dwds/test/chrome_proxy_service_test.dart
index 52f57523a..f410e2819 100644
--- a/dwds/test/chrome_proxy_service_test.dart
+++ b/dwds/test/chrome_proxy_service_test.dart
@@ -362,7 +362,7 @@ void main() {
 
     test('evaluateInFrame', () async {
       await expectLater(
-          service.evaluateInFrame(null, null, null), throwsRPCError);
+          service.evaluateInFrame(null, null, null), throwsSentinelException);
     });
 
     test('getAllocationProfile', () async {
@@ -406,7 +406,7 @@ void main() {
       });
 
       test('throws for invalid ids', () async {
-        expect(service.getIsolate('bad'), throwsArgumentError);
+        expect(service.getIsolate('bad'), throwsSentinelException);
       });
     });
 
@@ -545,7 +545,7 @@ void main() {
             list[4] = 100;
             return list;
       })()''';
-        return service.appInspectorProvider().jsEvaluate(expr);
+        return service.inspector.jsEvaluate(expr);
       }
 
       /// Helper to create a LinkedHashMap with 1001 entries, doing a direct JS eval.
@@ -561,7 +561,7 @@ void main() {
             const linkedMap = sdk.dart.dsend(sdk.collection.LinkedHashMap, "from", [map]);
             return linkedMap;
       })()''';
-        return service.appInspectorProvider().jsEvaluate(expr);
+        return service.inspector.jsEvaluate(expr);
       }
 
       test('Lists', () async {
diff --git a/dwds/test/debugger_test.dart b/dwds/test/debugger_test.dart
index 5c3c49f0f..bef2e0658 100644
--- a/dwds/test/debugger_test.dart
+++ b/dwds/test/debugger_test.dart
@@ -107,12 +107,12 @@ void main() async {
     debugger = await Debugger.create(
       webkitDebugger,
       null,
-      () => inspector,
       locations,
       skipLists,
       root,
     );
     inspector = FakeInspector();
+    debugger.updateInspector(inspector);
   });
 
   /// Test that we get expected variable values from a hard-coded
@@ -121,6 +121,7 @@ void main() async {
     final stackComputer = FrameComputer(debugger, frames1);
     final frames = await stackComputer.calculateFrames();
     expect(frames, isNotNull);
+    expect(frames, isNotEmpty);
 
     final firstFrame = frames[0];
     final frame1Variables = firstFrame.vars.map((each) => each.name).toList();
@@ -182,6 +183,7 @@ void main() async {
       // We need to provide an Isolate so that the code doesn't bail out on a null
       // check before it has a chance to throw.
       inspector = FakeInspector(fakeIsolate: simpleIsolate);
+      debugger.updateInspector(inspector);
     });
 
     test('errors in the zone are caught and logged', () async {
diff --git a/dwds/test/evaluate_common.dart b/dwds/test/evaluate_common.dart
index c62bfbbeb..797ab475f 100644
--- a/dwds/test/evaluate_common.dart
+++ b/dwds/test/evaluate_common.dart
@@ -509,7 +509,7 @@ void testAll({
           await expectLater(
               setup.service
                   .evaluateInFrame('bad', event.topFrame.index, 'local'),
-              throwsRPCError);
+              throwsSentinelException);
         });
       });
     });
diff --git a/dwds/test/fixtures/fakes.dart b/dwds/test/fixtures/fakes.dart
index 9662064bc..ec139d8fb 100644
--- a/dwds/test/fixtures/fakes.dart
+++ b/dwds/test/fixtures/fakes.dart
@@ -7,14 +7,15 @@
 import 'dart:async';
 
 import 'package:dwds/dwds.dart';
+import 'package:dwds/src/debugging/classes.dart';
 import 'package:dwds/src/debugging/execution_context.dart';
 import 'package:dwds/src/debugging/inspector.dart';
 import 'package:dwds/src/debugging/instance.dart';
+import 'package:dwds/src/debugging/libraries.dart';
 import 'package:dwds/src/debugging/modules.dart';
 import 'package:dwds/src/debugging/remote_debugger.dart';
 import 'package:dwds/src/debugging/webkit_debugger.dart';
 import 'package:dwds/src/loaders/strategy.dart';
-import 'package:dwds/src/utilities/domain.dart';
 import 'package:shelf/shelf.dart' as shelf;
 import 'package:vm_service/vm_service.dart';
 
@@ -42,23 +43,32 @@ Isolate get simpleIsolate => Isolate(
       isolateFlags: [],
     );
 
-class FakeInspector extends Domain implements AppInspector {
-  FakeInspector({this.fakeIsolate}) : super.forInspector();
+class FakeInspector implements AppInspector {
+  FakeInspector({this.fakeIsolate});
 
   Isolate fakeIsolate;
 
+  final _instanceHelper = InstanceHelper(null, null);
+
   @override
   Object noSuchMethod(Invocation invocation) {
     throw UnsupportedError('This is a fake');
   }
 
   @override
-  Future<Obj> getObject(String isolateId, String objectId,
-          {int offset, int count}) =>
+  Future<void> initialize(LibraryHelper libraryHelper, ClassHelper classHelper,
+          InstanceHelper instanceHelper) =>
       null;
 
   @override
-  Future<ScriptList> getScripts(String isolateId) => null;
+  Future<InstanceRef> instanceRefFor(Object value) =>
+      _instanceHelper.instanceRefFor(value);
+
+  @override
+  Future<Obj> getObject(String objectId, {int offset, int count}) => null;
+
+  @override
+  Future<ScriptList> getScripts() => null;
 
   @override
   Future<ScriptRef> scriptRefFor(String uri) =>
@@ -67,17 +77,11 @@ class FakeInspector extends Domain implements AppInspector {
   @override
   ScriptRef scriptWithId(String scriptId) => null;
 
-  @override
-  Isolate checkIsolate(String methodName, String isolateId) => fakeIsolate;
-
   @override
   Isolate get isolate => fakeIsolate;
 
   @override
   IsolateRef get isolateRef => null;
-
-  @override
-  InstanceHelper get instanceHelper => InstanceHelper(null);
 }
 
 class FakeSseConnection implements SseSocketConnection {
diff --git a/dwds/test/inspector_test.dart b/dwds/test/inspector_test.dart
index 7075406dc..e011addbc 100644
--- a/dwds/test/inspector_test.dart
+++ b/dwds/test/inspector_test.dart
@@ -28,8 +28,8 @@ void main() {
   setUpAll(() async {
     await context.setUp();
     final service = fetchChromeProxyService(context.debugConnection);
-    inspector = service.appInspectorProvider();
-    debugger = inspector.debugger;
+    inspector = service.inspector;
+    debugger = await service.debuggerFuture;
   });
 
   tearDownAll(() async {
@@ -50,18 +50,18 @@ void main() {
 
   test('send toString', () async {
     final remoteObject = await libraryPublicFinal();
-    final toString = await inspector.invokeMethod(remoteObject, 'toString', []);
+    final toString =
+        await inspector.invoke(remoteObject.objectId, 'toString', []);
     expect(toString.value, 'A test class with message world');
   });
 
   group('getObject', () {
     test('for class with generic', () async {
-      final isolateId = inspector.isolate.id;
       final remoteObject = await libraryPublicFinal();
-      final instance = await inspector.getObject(
-          isolateId, remoteObject.objectId) as Instance;
+      final instance =
+          await inspector.getObject(remoteObject.objectId) as Instance;
       final classRef = instance.classRef;
-      final clazz = await inspector.getObject(isolateId, classRef.id) as Class;
+      final clazz = await inspector.getObject(classRef.id) as Class;
       expect(clazz.name, 'MyTestClass<dynamic>');
     });
   });
@@ -103,18 +103,16 @@ void main() {
     // We test these here because the test fixture has more complicated members
     // to exercise.
 
-    String isolateId;
     LibraryRef bootstrapLibrary;
     RemoteObject instance;
 
     setUp(() async {
-      isolateId = inspector.isolate.id;
       bootstrapLibrary = inspector.isolate.rootLib;
       instance = await libraryPublicFinal();
     });
 
     test('invoke top-level private', () async {
-      final remote = await inspector.invoke(isolateId, bootstrapLibrary.id,
+      final remote = await inspector.invoke(bootstrapLibrary.id,
           '_libraryPrivateFunction', [dartIdFor(2), dartIdFor(3)]);
       expect(
           remote,
@@ -123,8 +121,8 @@ void main() {
     });
 
     test('invoke instance private', () async {
-      final remote = await inspector.invoke(isolateId, instance.objectId,
-          'privateMethod', [dartIdFor('some string')]);
+      final remote = await inspector.invoke(
+          instance.objectId, 'privateMethod', [dartIdFor('some string')]);
       expect(
           remote,
           const TypeMatcher<RemoteObject>().having((instance) => instance.value,
@@ -133,7 +131,7 @@ void main() {
 
     test('invoke instance method with object parameter', () async {
       final remote = await inspector
-          .invoke(isolateId, instance.objectId, 'equals', [instance.objectId]);
+          .invoke(instance.objectId, 'equals', [instance.objectId]);
       expect(
           remote,
           const TypeMatcher<RemoteObject>()
@@ -142,8 +140,8 @@ void main() {
 
     test('invoke instance method with object parameter 2', () async {
       final libraryPrivateList = await libraryPrivate();
-      final remote = await inspector.invoke(isolateId, instance.objectId,
-          'equals', [libraryPrivateList.objectId]);
+      final remote = await inspector
+          .invoke(instance.objectId, 'equals', [libraryPrivateList.objectId]);
       expect(
           remote,
           const TypeMatcher<RemoteObject>()
@@ -151,8 +149,7 @@ void main() {
     });
 
     test('invoke closure stored in an instance field', () async {
-      final remote =
-          await inspector.invoke(isolateId, instance.objectId, 'closure', []);
+      final remote = await inspector.invoke(instance.objectId, 'closure', []);
       expect(
           remote,
           const TypeMatcher<RemoteObject>()
@@ -161,8 +158,7 @@ void main() {
 
     test('invoke a torn-off method', () async {
       final toString = await inspector.loadField(instance, 'tornOff');
-      final result =
-          await inspector.invoke(isolateId, toString.objectId, 'call', []);
+      final result = await inspector.invoke(toString.objectId, 'call', []);
       expect(
           result,
           const TypeMatcher<RemoteObject>().having((instance) => instance.value,
diff --git a/dwds/test/instance_test.dart b/dwds/test/instance_test.dart
index d0548f3de..9d44aa9fa 100644
--- a/dwds/test/instance_test.dart
+++ b/dwds/test/instance_test.dart
@@ -7,7 +7,6 @@
 import 'package:dwds/src/connections/debug_connection.dart';
 import 'package:dwds/src/debugging/debugger.dart';
 import 'package:dwds/src/debugging/inspector.dart';
-import 'package:dwds/src/debugging/instance.dart';
 import 'package:dwds/src/loaders/strategy.dart';
 import 'package:test/test.dart';
 import 'package:vm_service/vm_service.dart';
@@ -23,14 +22,12 @@ WipConnection get tabConnection => context.tabConnection;
 void main() {
   AppInspector inspector;
   Debugger debugger;
-  InstanceHelper instanceHelper;
 
   setUpAll(() async {
     await context.setUp();
     final chromeProxyService = fetchChromeProxyService(context.debugConnection);
-    inspector = chromeProxyService.appInspectorProvider();
-    debugger = inspector.debugger;
-    instanceHelper = inspector.instanceHelper;
+    inspector = chromeProxyService.inspector;
+    debugger = await chromeProxyService.debuggerFuture;
   });
 
   tearDownAll(() async {
@@ -56,7 +53,7 @@ void main() {
     test('for a null', () async {
       final remoteObject = await libraryPublicFinal();
       final nullVariable = await inspector.loadField(remoteObject, 'notFinal');
-      final ref = await instanceHelper.instanceRefFor(nullVariable);
+      final ref = await inspector.instanceRefFor(nullVariable);
       expect(ref.valueAsString, 'null');
       expect(ref.kind, InstanceKind.kNull);
       final classRef = ref.classRef;
@@ -67,7 +64,7 @@ void main() {
     test('for a double', () async {
       final remoteObject = await libraryPublicFinal();
       final count = await inspector.loadField(remoteObject, 'count');
-      final ref = await instanceHelper.instanceRefFor(count);
+      final ref = await inspector.instanceRefFor(count);
       expect(ref.valueAsString, '0');
       expect(ref.kind, InstanceKind.kDouble);
       final classRef = ref.classRef;
@@ -78,7 +75,7 @@ void main() {
     test('for a class', () async {
       final remoteObject = await libraryPublicFinal();
       final count = await inspector.loadField(remoteObject, 'myselfField');
-      final ref = await instanceHelper.instanceRefFor(count);
+      final ref = await inspector.instanceRefFor(count);
       expect(ref.kind, InstanceKind.kPlainInstance);
       final classRef = ref.classRef;
       expect(classRef.name, 'MyTestClass<dynamic>');
@@ -93,7 +90,7 @@ void main() {
       final properties = await debugger.getProperties(remoteObject.objectId);
       final closure =
           properties.firstWhere((property) => property.name == 'closure');
-      final instanceRef = await instanceHelper.instanceRefFor(closure.value);
+      final instanceRef = await inspector.instanceRefFor(closure.value);
       final functionName = instanceRef.closureFunction.name;
       // Older SDKs do not contain function names
       if (functionName != 'Closure') {
@@ -104,7 +101,7 @@ void main() {
 
     test('for a list', () async {
       final remoteObject = await libraryPublic();
-      final ref = await instanceHelper.instanceRefFor(remoteObject);
+      final ref = await inspector.instanceRefFor(remoteObject);
       expect(ref.length, greaterThan(0));
       expect(ref.kind, InstanceKind.kList);
       expect(ref.classRef.name, 'List<String>');
@@ -113,7 +110,7 @@ void main() {
     test('for map', () async {
       final remoteObject =
           await inspector.jsEvaluate(libraryVariableExpression('map'));
-      final ref = await instanceHelper.instanceRefFor(remoteObject);
+      final ref = await inspector.instanceRefFor(remoteObject);
       expect(ref.length, 2);
       expect(ref.kind, InstanceKind.kMap);
       expect(ref.classRef.name, 'LinkedMap<Object, Object>');
@@ -122,7 +119,7 @@ void main() {
     test('for an IdentityMap', () async {
       final remoteObject =
           await inspector.jsEvaluate(libraryVariableExpression('identityMap'));
-      final ref = await instanceHelper.instanceRefFor(remoteObject);
+      final ref = await inspector.instanceRefFor(remoteObject);
       expect(ref.length, 2);
       expect(ref.kind, InstanceKind.kMap);
       expect(ref.classRef.name, 'IdentityMap<String, int>');
@@ -132,7 +129,7 @@ void main() {
   group('instance', () {
     test('for class object', () async {
       final remoteObject = await libraryPublicFinal();
-      final instance = await instanceHelper.instanceFor(remoteObject);
+      final instance = await inspector.instanceFor(remoteObject);
       expect(instance.kind, InstanceKind.kPlainInstance);
       final classRef = instance.classRef;
       expect(classRef, isNotNull);
@@ -159,7 +156,7 @@ void main() {
       final properties = await debugger.getProperties(remoteObject.objectId);
       final closure =
           properties.firstWhere((property) => property.name == 'closure');
-      final instance = await instanceHelper.instanceFor(closure.value);
+      final instance = await inspector.instanceFor(closure.value);
       expect(instance.kind, InstanceKind.kClosure);
       expect(instance.classRef.name, 'Closure');
     });
@@ -168,7 +165,7 @@ void main() {
       final libraryRemoteObject = await libraryPublicFinal();
       final fieldRemoteObject =
           await inspector.loadField(libraryRemoteObject, 'myselfField');
-      final instance = await instanceHelper.instanceFor(fieldRemoteObject);
+      final instance = await inspector.instanceFor(fieldRemoteObject);
       expect(instance.kind, InstanceKind.kPlainInstance);
       final classRef = instance.classRef;
       expect(classRef, isNotNull);
@@ -177,7 +174,7 @@ void main() {
 
     test('for a list', () async {
       final remote = await libraryPublic();
-      final instance = await instanceHelper.instanceFor(remote);
+      final instance = await inspector.instanceFor(remote);
       expect(instance.kind, InstanceKind.kList);
       final classRef = instance.classRef;
       expect(classRef, isNotNull);
@@ -189,7 +186,7 @@ void main() {
     test('for a map', () async {
       final remote =
           await inspector.jsEvaluate(libraryVariableExpression('map'));
-      final instance = await instanceHelper.instanceFor(remote);
+      final instance = await inspector.instanceFor(remote);
       expect(instance.kind, InstanceKind.kMap);
       final classRef = instance.classRef;
       expect(classRef.name, 'LinkedMap<Object, Object>');
@@ -204,7 +201,7 @@ void main() {
     test('for an identityMap', () async {
       final remote =
           await inspector.jsEvaluate(libraryVariableExpression('identityMap'));
-      final instance = await instanceHelper.instanceFor(remote);
+      final instance = await inspector.instanceFor(remote);
       expect(instance.kind, InstanceKind.kMap);
       final classRef = instance.classRef;
       expect(classRef.name, 'IdentityMap<String, int>');
@@ -216,7 +213,7 @@ void main() {
       // The VM only uses kind List for SDK lists, and we follow that.
       final remote =
           await inspector.jsEvaluate(libraryVariableExpression('notAList'));
-      final instance = await instanceHelper.instanceFor(remote);
+      final instance = await inspector.instanceFor(remote);
       expect(instance.kind, InstanceKind.kPlainInstance);
       final classRef = instance.classRef;
       expect(classRef.name, 'NotReallyAList');
diff --git a/dwds/test/variable_scope_test.dart b/dwds/test/variable_scope_test.dart
index bfb81e685..7953d7f3c 100644
--- a/dwds/test/variable_scope_test.dart
+++ b/dwds/test/variable_scope_test.dart
@@ -183,8 +183,7 @@ void main() {
 
     test('evaluateJsOnCallFrame', () async {
       stack = await breakAt('nestedFunction', mainScript);
-      final inspector = service.appInspectorProvider();
-      final debugger = inspector.debugger;
+      final debugger = await service.debuggerFuture;
       final parameter =
           await debugger.evaluateJsOnCallFrameIndex(0, 'parameter');
       expect(parameter.value, matches(RegExp(r'\d+ world')));
diff --git a/dwds/web/reloader/require_restarter.dart b/dwds/web/reloader/require_restarter.dart
index 41850ebd6..6124c551e 100644
--- a/dwds/web/reloader/require_restarter.dart
+++ b/dwds/web/reloader/require_restarter.dart
@@ -219,11 +219,16 @@ class RequireRestarter implements Restarter {
   Future<void> _reloadModule(String moduleId) {
     final completer = Completer();
     final stackTrace = StackTrace.current;
-    requireLoader.forceLoadModule(moduleId, allowInterop(() {
-      completer.complete();
-    }),
-        allowInterop((e) => completer.completeError(
-            HotReloadFailedException(e.message), stackTrace)));
+    requireLoader.forceLoadModule(
+      moduleId,
+      allowInterop(() {
+        completer.complete();
+      }),
+      allowInterop((e) {
+        completer.completeError(
+            HotReloadFailedException(e.message), stackTrace);
+      }),
+    );
     return completer.future;
   }