implement dirty checking for @observable objects

pkg/observe/test/utils.dart

Index: pkg/observe/test/utils.dart
diff --git a/pkg/observe/test/utils.dart b/pkg/observe/test/utils.dart
deleted file mode 100644
index dafedc167e96861cad53acea3e43818d64fd1140..0000000000000000000000000000000000000000
--- a/pkg/observe/test/utils.dart
+++ /dev/null
@@ -1,12 +0,0 @@
-// Copyright (c) 2013, 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.
-
-library observe.test.utils;
-
-import 'package:unittest/unittest.dart';
-
-// TODO(jmesserly): use matchers when we have a way to compare ChangeRecords.
-// For now just use the toString.
-expectChanges(actual, expected, {reason}) =>
-    expect('$actual', '$expected', reason: reason);