introduce web_components pkg for consolidated polyfills

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 13 matching lines @@
 
   void leftView() {
     invocations.add('left');
   }
 
   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');
-  }
-}
-
 main() {
   useHtmlIndividualConfiguration();
 
   // Adapted from Blink's
   // fast/dom/custom/entered-left-document.html test.
 
   var docA = document;
   var docB = document.implementation.createHtmlDocument('');
 
   var nullSanitizer = new NullTreeSanitizer();
 
   var registeredTypes = false;
-  setUp(() {
-    return loadPolyfills().then((_) {
-      if (registeredTypes) {
-        return;
-      }
-      registeredTypes = true;
-      document.register('x-a', Foo);
-    });
-  });
+  setUp(() => customElementsReady.then((_) {
+    if (registeredTypes) return;
+    registeredTypes = true;
+    document.register('x-a', Foo);
+  }));
 
   group('standard_events', () {
     var a;
     setUp(() {
       invocations = [];
     });
 
     test('Created', () {
       a = new Element.tag('x-a');
       expect(invocations, ['created']);
@@ skipping 163 matching lines @@
       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');
     });
   });
 }