Fixing Element.shadowRoot to work with webkitShadowRoot

tests/html/shadowroot_test.dart

 // Copyright (c) 2012, 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 ShadowRootTest;
 import '../../pkg/unittest/lib/unittest.dart';
 import '../../pkg/unittest/lib/html_config.dart';
 import 'dart:html';
 
 main() {
   useHtmlConfiguration();
 
   var isShadowRoot =
       predicate((x) => x is ShadowRoot, 'is a ShadowRoot');
 
   test('ShadowRoot supported', () {
     var isSupported = ShadowRoot.supported;
 
     // If it's supported, then it should work. Otherwise should fail.
     if (isSupported) {
-      var shadowRoot = new DivElement().createShadowRoot();
+      var div = new DivElement();
+      var shadowRoot = div.createShadowRoot();
       expect(shadowRoot, isShadowRoot);
+      expect(div.shadowRoot, shadowRoot);
     } else {
       expect(() => new DivElement().createShadowRoot(), throws);
     }
   });
 }