Have Element::ensureUserAgentShadowRoot() return a reference

Source/core/html/HTMLDetailsElement.h

 /*
  * Copyright (C) 2010, 2011 Nokia Corporation and/or its subsidiary(-ies)
  *
  * 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,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 20 matching lines @@
     void toggleOpen();
 
     Element* findMainSummary() const;
 
 private:
     HTMLDetailsElement(const QualifiedName&, Document&);
 
     virtual RenderObject* createRenderer(RenderStyle*);
     virtual bool childShouldCreateRenderer(const Node& child) const OVERRIDE;
     virtual void parseAttribute(const QualifiedName&, const AtomicString&) OVERRIDE;
-    virtual void didAddUserAgentShadowRoot(ShadowRoot*) OVERRIDE;
+    virtual void didAddUserAgentShadowRoot(ShadowRoot&) OVERRIDE;
     virtual bool isInteractiveContent() const OVERRIDE;
 
     bool m_isOpen;
 };
 
 inline bool isHTMLDetailsElement(const Node* node)
 {
     return node->hasTagName(HTMLNames::detailsTag);
 }
 
 inline bool isHTMLDetailsElement(const Element* element)
 {
     return element->hasTagName(HTMLNames::detailsTag);
 }
 
 DEFINE_NODE_TYPE_CASTS(HTMLDetailsElement, hasTagName(HTMLNames::detailsTag));
 
 } // namespace WebCore
 
 #endif // HTMLDetailsElement_h