[polymer.dart] fix *Changed observers inheriting

pkg/polymer/test/property_change_test.dart

+// 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 polymer.test.property_change_test;
+
+import 'dart:async';
+import 'dart:html';
+import 'package:polymer/polymer.dart';
+import 'package:unittest/unittest.dart';
+import 'package:unittest/html_config.dart';
+import 'package:unittest/matcher.dart';
+
+// Dart note: this is a tad different from the JS code. We don't support putting
+// expandos on Dart objects and then observing them. On the other hand, we want
+// to make sure that superclass observers are correctly detected.
+
+final _zonk = new Completer();
+final _bar = new Completer();
+
+class XBase extends PolymerElement {
+  @observable String zonk = '';
+
+  XBase.created() : super.created();
+
+  zonkChanged() {
+    expect(zonk, 'zonk', reason: 'change calls *Changed on superclass');
+    _zonk.complete();
+  }
+}
+
+@CustomTag('x-test')
+class XTest extends XBase {
+  @observable String bar = '';
+
+  XTest.created() : super.created();
+
+  ready() {
+    bar = 'bar';
+    new Future(() { zonk = 'zonk'; });
+  }
+
+  barChanged() {
+    expect(bar, 'bar', reason: 'change in ready calls *Changed');
+    _bar.complete();
+  }
+}
+
+main() {
+  initPolymer();
+  useHtmlConfiguration();
+
+  setUp(() => Polymer.onReady);
+
+  test('bar change detected', () => _bar.future);
+  test('zonk change detected', () => _zonk.future);
+}