Remove output unit field from code-span, it is redundant with output unit in the enclosing entity (#64)

Author: sigmundch

lib/binary_codec.dart

@@ -128,7 +128,6 @@ class BinaryPrinter implements InfoVisitor<void> {
   }
 
   _visitCodeSpan(CodeSpan code) {
-    _writeOutputOrNull(code.outputUnit);
     sink.writeIntOrNull(code.start);
     sink.writeIntOrNull(code.end);
     sink.writeStringOrNull(code.text);
@@ -372,7 +371,6 @@ class BinaryReader {
 
   CodeSpan _readCodeSpan() {
     return new CodeSpan()
-      ..outputUnit = _readOutputOrNull()
       ..start = source.readIntOrNull()
       ..end = source.readIntOrNull()
       ..text = source.readStringOrNull();

lib/info.dart

@@ -237,21 +237,21 @@ class ClassInfo extends BasicInfo {
   T accept<T>(InfoVisitor<T> visitor) => visitor.visitClass(this);
 }
 
-/// Details about generated code spans.
+/// A code span of generated code. A [CodeSpan] object is associated with a
+/// single [BasicInfo]. The offsets in the span corresponds to offsets on the
+/// file of [BasicInfo.outputUnit].
 class CodeSpan {
-  /// File where the code was generated.
-  OutputUnitInfo outputUnit;
-
   /// Start offset in the generated file.
   int start;
 
   /// end offset in the generated file.
   int end;
 
-  /// The actual code.
+  /// The actual code (optional, blank when using a compact representation of
+  /// the encoding).
   String text;
 
-  CodeSpan({this.outputUnit, this.start, this.end, this.text});
+  CodeSpan({this.start, this.end, this.text});
 }
 
 /// Information about a constant value.

lib/json_info_codec.dart

@@ -310,16 +310,13 @@ class JsonToAllInfoConverter extends Converter<Map<String, dynamic>, AllInfo> {
   List<CodeSpan> parseCode(dynamic json) {
     // backwards compatibility with format 5.1:
     if (json is String) {
-      return [
-        new CodeSpan(outputUnit: null, start: null, end: null, text: json)
-      ];
+      return [new CodeSpan(start: null, end: null, text: json)];
     }
 
     if (json is List) {
       return json.map((dynamic value) {
         Map<String, dynamic> jsonCode = value;
         return new CodeSpan(
-            outputUnit: parseId(jsonCode['outputUnit']),
             start: jsonCode['start'],
             end: jsonCode['end'],
             text: jsonCode['text']);
@@ -570,9 +567,6 @@ class AllInfoToJsonConverter extends Converter<AllInfo, Map>
   List<Object> _serializeCode(List<CodeSpan> code) {
     return code
         .map<Object>((c) => {
-              'outputUnit': c.outputUnit != null
-                  ? idFor(c.outputUnit).serializedId
-                  : null,
               'start': c.start,
               'end': c.end,
               'text': c.text,