introduce web_components pkg for consolidated polyfills

pkg/template_binding/test/custom_element_bindings_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_binding.test.custom_element_bindings_test;
 
 import 'dart:async';
 import 'dart:html';
-import 'package:custom_element/polyfill.dart';
 import 'package:template_binding/template_binding.dart';
 import 'package:observe/observe.dart';
 import 'package:unittest/html_config.dart';
 import 'package:unittest/unittest.dart';
+import 'package:web_components/polyfill.dart';
 import 'utils.dart';
 
 Future _registered;
 
 main() => dirtyCheckZone().run(() {
   useHtmlConfiguration();
 
-  _registered = loadCustomElementPolyfill().then((_) {
+  _registered = customElementsReady.then((_) {
     document.register('my-custom-element', MyCustomElement);
     document.register('with-attrs-custom-element', WithAttrsCustomElement);
   });
 
   group('Custom Element Bindings', customElementBindingsTest);
 });
 
 customElementBindingsTest() {
   setUp(() {
     document.body.append(testDiv = new DivElement());
@@ skipping 207 matching lines @@
 
   void addAll(Map<K, V> other) => _map.addAll(other);
   void clear() => _map.clear();
   void forEach(void f(K key, V value)) => _map.forEach(f);
   Iterable<K> get keys => _map.keys;
   Iterable<V> get values => _map.values;
   int get length => _map.length;
   bool get isEmpty => _map.isEmpty;
   bool get isNotEmpty => _map.isNotEmpty;
 }