[dart2js] Migrate some easy files to nnbd.

Change-Id: Ib61264fa3febd9067909292d5a4468a9044118a2
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/247286
Reviewed-by: Stephen Adams <[email protected]>
Commit-Queue: Nate Biggs <[email protected]>

Author: natebiggs

pkg/compiler/lib/src/ir/cached_static_type.dart

@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.10
-
 import 'package:kernel/ast.dart' as ir;
 import 'package:kernel/type_environment.dart' as ir;
 import 'static_type_base.dart';
@@ -25,24 +23,13 @@ class CachedStaticType extends StaticTypeBase implements StaticTypeProvider {
       : super(staticTypeContext.typeEnvironment);
 
   @override
-  ir.DartType getStaticType(ir.Expression node) {
-    ir.DartType type = node.accept(this);
-    assert(type != null, "No static type found for ${node.runtimeType}.");
-    return type;
-  }
+  ir.DartType getStaticType(ir.Expression node) => node.accept(this)!;
 
   @override
-  ir.DartType getForInIteratorType(ir.ForInStatement node) {
-    ir.DartType type = _cache.getForInIteratorType(node);
-    assert(type != null, "No for-in iterator type found for ${node}.");
-    return type;
-  }
+  ir.DartType getForInIteratorType(ir.ForInStatement node) =>
+      _cache.getForInIteratorType(node)!;
 
-  ir.DartType _getStaticType(ir.Expression node) {
-    ir.DartType type = _cache[node];
-    assert(type != null, "No static type cached for ${node.runtimeType}.");
-    return type;
-  }
+  ir.DartType _getStaticType(ir.Expression node) => _cache[node]!;
 
   @override
   ir.DartType visitVariableGet(ir.VariableGet node) => _getStaticType(node);

pkg/compiler/lib/src/universe/feature.dart

@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.10
-
 // TODO(sigmund): rename universe => world
 /// Describes individual features that may be seen in a program. Most features
 /// can be described only by name using the [Feature] enum, some features are
@@ -249,7 +247,7 @@ class GenericInstantiation {
 
   factory GenericInstantiation.readFromDataSource(DataSourceReader source) {
     source.begin(tag);
-    DartType functionType = source.readDartType();
+    final functionType = source.readDartType() as FunctionType;
     List<DartType> typeArguments = source.readDartTypes();
     source.end(tag);
     return GenericInstantiation(functionType, typeArguments);