Fix issues with protobuf equality comparisons

test/map_mixin_test.dart

 #!/usr/bin/env dart
 // Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
 // 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.
 
 // Unit tests for PbMapMixin.
 // There are more tests in the dart-protoc-plugin package.
 library map_mixin_test;
 
 import 'dart:collection' show MapMixin;
 
 import 'package:protobuf/src/protobuf/mixins/map_mixin.dart';
 import 'package:test/test.dart' show test, expect, predicate, same, throws;
 
-import 'mock_util.dart' show MockMessage;
+import 'mock_util.dart' show MockMessage, mockInfo;
 
 // A minimal protobuf implementation compatible with PbMapMixin.
 class Rec extends MockMessage with MapMixin, PbMapMixin {
-  get className => "Rec";
-  Rec create() => new Rec();
+  get info_ => _info;
+  static final _info = mockInfo("Rec", () => new Rec());
 
   @override
   String toString() => "Rec(${val}, \"${str}\")";
 }
 
 main() {
   test('PbMapMixin methods return default field values', () {
     var r = new Rec();
 
     expect(r.isEmpty, false);
@@ skipping 27 matching lines @@
     var child = new Rec();
     r["child"] = child;
     expect(r.child, same(child));
     expect(r["child"], same(child));
 
     expect(() => r["int32s"] = 123, throws);
     r["int32s"].add(123);
     expect(r["int32s"], [123]);
     expect(r["int32s"], same(r["int32s"]));
   });
+
+  test('operator[]== works for Map mixin', () {
+    var a = new Rec();
+    expect(a == a, true);
+    expect(a == {}, false);
+    expect({} == a, false);
+
+    var b = new Rec();
+    expect(a.info_ == b.info_, true, reason: "BuilderInfo should be the same");
+    expect(a == b, true);
+
+    a.val = 123;
+    expect(a == b, false);
+    b.val = 123;
+    expect(a == b, true);
+
+    a.child = new Rec();
+    expect(a == b, false);
+    b.child = new Rec();
+    expect(a == b, true);
+  });
+
+  test("protobuf doesn't compare equal to a map with the same values", () {
+    var a = new Rec();
+    expect(a == new Map.from(a), false);
+    expect(new Map.from(a) == a, false);
+  });
+
+  test("reading protobuf values shouldn't change equality", () {
+    var a = new Rec();
+    var b = new Rec();
+    expect(a == b, true);
+    new Map.from(a);
+    expect(a == b, true);
+  });
 }