Only allow one shadowRoot.

sky/engine/core/dom/Element.idl

 /*
  * Copyright (C) 2006, 2007, 2009 Apple Inc. All rights reserved.
  * Copyright (C) 2006 Samuel Weinig <sam.weinig@gmail.com>
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
@@ skipping 46 matching lines @@
     readonly attribute long scrollHeight;
 
     void focus();
     void blur();
     void scrollIntoView(optional boolean alignWithTop);
 
     [MeasureAs=ElementScrollIntoViewIfNeeded] void scrollIntoViewIfNeeded(optional boolean centerIfNeeded);
 
     [PerWorldBindings] readonly attribute DOMTokenList classList;
 
-    [RaisesException, MeasureAs=ElementCreateShadowRoot] ShadowRoot createShadowRoot();
+    [RaisesException] ShadowRoot ensureShadowRoot();
     [PerWorldBindings] readonly attribute ShadowRoot shadowRoot;
     NodeList getDestinationInsertionPoints();
 
     // CSSOM View Module API
     ClientRectList getClientRects();
     ClientRect getBoundingClientRect();
 };
 
 Element implements ParentNode;
 Element implements ChildNode;