introduce web_components pkg for consolidated polyfills

tests/html/custom/template_wrappers_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 template_wrappers_test;
 
 import 'dart:async';
 import 'dart:html';
 import 'dart:js' as js;
 import 'package:unittest/html_config.dart';
 import 'package:unittest/unittest.dart';
 import '../utils.dart';
 
 int createdCount = 0;
 
 class CustomElement extends HtmlElement {
   CustomElement.created() : super.created() {
     ++createdCount;
   }
 
   void checkCreated() {
   }
 }
 
-// Pump custom events polyfill events.
-void customElementsTakeRecords() {
-  if (js.context != null && js.context.hasProperty('CustomElements')) {
-    js.context['CustomElements'].callMethod('takeRecords');
-  }
-}
-
 main() {
   useHtmlConfiguration();
 
-  setUp(loadPolyfills);
+  setUp(customElementsReady);
 
   test('element is upgraded once', () {
 
     expect(createdCount, 0);
     document.register('x-custom', CustomElement);
     expect(createdCount, 1);
 
     forceGC();
 
     return new Future.delayed(new Duration(milliseconds: 50)).then((_) {
@@ skipping 27 matching lines @@
 }
 
 
 void forceGC() {
   var N = 1000000;
   var M = 100;
   for (var i = 0; i < M; ++i) {
     var l = new List(N);
   }
 }