Revert "Revert "Dart2js support for custom element lifecycle events""

tests/html/custom/constructor_calls_created_synchronously_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 constructor_calls_created_synchronously_test;
 import 'package:unittest/unittest.dart';
 import 'package:unittest/html_config.dart';
 import 'dart:html';
+import '../utils.dart';
 
 class A extends HtmlElement {
   static final tag = 'x-a';
   factory A() => new Element.tag(tag);
 
   static int ncallbacks = 0;
 
   void created() {
     ncallbacks++;
   }
 }
 
-loadPolyfills() {
-  if (!document.supportsRegister) {
-    // Cache blocker is a workaround for:
-    // https://code.google.com/p/dart/issues/detail?id=11834
-    var cacheBlocker = new DateTime.now().millisecondsSinceEpoch;
-    return HttpRequest.getString('/root_dart/pkg/custom_element/lib/'
-      'custom-elements.debug.js?cacheBlock=$cacheBlocker').then((code) {
-      document.head.children.add(new ScriptElement()..text = code);
-    });
-  }
-}
-
 main() {
   useHtmlConfiguration();
 
   // Adapted from Blink's
   // fast/dom/custom/constructor-calls-created-synchronously test.
 
   setUp(loadPolyfills);
 
   test('createdCallback', () {
     document.register(A.tag, A);
     var x = new A();
     expect(A.ncallbacks, 1);
   });
 }