update elements and fix some bugs

test/iron_a11y_announcer_test.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.
 @TestOn('browser')
 library polymer_elements.test.iron_a11y_announcer_test;
 
 import 'dart:async';
 import 'dart:html';
+import 'dart:js';
 import 'package:polymer_elements/iron_a11y_announcer.dart';
 import 'package:web_components/web_components.dart';
 import 'package:test/test.dart';
 
 main() async {
   await initWebComponents();
 
   group('<iron-a11y-announcer', () {
     IronA11yAnnouncer announcer;
 
     setUp(() {
       announcer = new IronA11yAnnouncer();
     });
 
     test('announces when there is an iron-announce event', () async {
-      var event = new CustomEvent('iron-announce',
-          canBubble: true, detail: {'text': 'foo'});
-      document.body.dispatchEvent(event);
+      announcer.fire('iron-announce',
+          detail: {'text': 'foo'}, node: document.body);
       // Text isn't set for 100ms
       await new Future.delayed(new Duration(milliseconds: 200), () {});
       expect(announcer.jsElement['_text'], 'foo');
     });
   });
 }