introduce web_components pkg for consolidated polyfills

tests/html/utils.dart

 library TestUtils;
 
 import 'dart:async';
 import 'dart:html';
 import 'dart:js' as js;
 import 'dart:typed_data';
 import 'package:unittest/unittest.dart';
+export 'package:web_components/polyfill.dart';
 
 /**
  * Verifies that [actual] has the same graph structure as [expected].
  * Detects cycles and DAG structure in Maps and Lists.
  */
 verifyGraph(expected, actual) {
   var eItems = [];
   var aItems = [];
 
   message(path, reason) => path == ''
@@ skipping 136 matching lines @@
     for (var key in aE.attributes.keys) {
       expect(aE.attributes[key], bE.attributes[key],
           reason: '$path attribute [$key] values differ');
     }
   }
   for (var i = 0; i < a.nodes.length; ++i) {
     validateNodeTree(a.nodes[i], b.nodes[i], '$path[$i].');
   }
 }
 
-Future loadCustomElementPolyfill() {
-  if (!document.supportsRegister) {
-    var script = new ScriptElement()
-        ..src = '/packages/custom_element/custom-elements.debug.js';
-    document.head.append(script);
-    return document.on['WebComponentsReady'].first;
-  }
-  return new Future.value();
-}
-
-Future loadPolyfills() {
-  return loadCustomElementPolyfill();
-}
-
 /**
  * Upgrade all custom elements in the subtree which have not been upgraded.
  *
  * This is needed to cover timing scenarios which the custom element polyfill
  * does not cover.
  */
 void upgradeCustomElements(Node node) {
   if (js.context.hasProperty('CustomElements') &&
       js.context['CustomElements'].hasProperty('upgradeAll')) {
     js.context['CustomElements'].callMethod('upgradeAll', [node]);
   }
 }