regenerate fixed custom_elements polyfill

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';
 
 /**
  * Verifies that [actual] has the same graph structure as [expected].
@@ skipping 145 matching lines @@
           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) {
-    if (!MutationObserver.supported) {
-      var script = new ScriptElement()
-          ..src = '/packages/mutation_observer/mutation_observer.js';
-      document.head.append(script);
-    }
     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]);
   }
 }