Fixing up WebComponents types & tests

tests/html/shadow_dom_layout_test.dart

 // Copyright (c) 2011, 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 ShadowDOMTest;
 
 import 'dart:html';
 
 // Test that children of a shadow host get distributed properly to the
 // insertion points of a shadow subtree. Output should be three boxes,
 // ordered blue, red, green down the page.
 main() {
   var div = new DivElement();
   document.body.children.add(div);
 
   // build some DOM elements
   var bluebox = _colorBox('blue', 40, 20);
   bluebox.classes.add('foo');
   var redbox = _colorBox('red', 30, 30);
   var greenbox = _colorBox('green', 60, 10);
 
   // assemble DOM
-  var sRoot = div.webkitCreateShadowRoot();
+  var sRoot = div.createShadowRoot();
   sRoot.nodes.add(new Element.html('<content select=".foo"></content>'));
   sRoot.nodes.add(redbox);
   sRoot.nodes.add(new Element.tag('content'));
 
   div.nodes.add(bluebox);
   div.nodes.add(greenbox);
 }
 
 DivElement _colorBox(String color, int width, int height) {
   var style = ('background-color:$color; '
       'width:${width}px; height:${height}px;');
   return new Element.html('<div style="$style"></div>');
 }