Implementing CustomElement's attributeChanged callback.

tests/html/custom/entered_left_view_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 entered_left_view_test;
 
 import 'dart:async';
 import 'dart:html';
 import 'dart:js' as js;
 import 'package:unittest/html_individual_config.dart';
@@ skipping 10 matching lines @@
   }
 
   void enteredView() {
     invocations.add('entered');
   }
 
   void leftView() {
     invocations.add('left');
   }
 
-  void attributeChanged() {
+  void attributeChanged(String name, String oldValue, String newValue) {
     invocations.add('attribute changed');
   }
 }
 
 // Pump custom events polyfill events.
 void customElementsTakeRecords() {
   if (js.context.hasProperty('CustomElements')) {
     js.context['CustomElements'].callMethod('takeRecords');
   }
 }
@@ skipping 196 matching lines @@
       Platform.upgradeCustomElements(div);
       invocations = [];
       document.body.append(div);
       customElementsTakeRecords();
       expect(invocations, ['entered'],
           reason: 'the entered callback should be invoked when inserted into a '
           'document with a view as part of a subtree');
     });
   });
 }