Make ElementRareData::ensureShadow() return a reference

Source/core/dom/Element.h

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Peter Kelly (pmk@post.com)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2013 Apple Inc. All rights reserved.
  *
  * 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
@@ skipping 421 matching lines @@
     virtual void copyNonAttributePropertiesFromElement(const Element&) { }
 
     virtual void attach(const AttachContext& = AttachContext()) OVERRIDE;
     virtual void detach(const AttachContext& = AttachContext()) OVERRIDE;
     virtual RenderObject* createRenderer(RenderStyle*);
     virtual bool rendererIsNeeded(const RenderStyle&);
     bool recalcStyle(StyleRecalcChange);
     void didAffectSelector(AffectedSelectorMask);
 
     ElementShadow* shadow() const;
-    ElementShadow* ensureShadow();
+    ElementShadow& ensureShadow();
     PassRefPtr<ShadowRoot> createShadowRoot(ExceptionState&);
     ShadowRoot* shadowRoot() const;
 
     bool hasAuthorShadowRoot() const { return shadowRoot(); }
     virtual void didAddShadowRoot(ShadowRoot&);
     ShadowRoot* userAgentShadowRoot() const;
     ShadowRoot* ensureUserAgentShadowRoot();
     virtual const AtomicString& shadowPseudoId() const { return !part().isEmpty() ? part() : pseudo(); }
 
     RenderStyle* computedStyle(PseudoId = NOPSEUDO);
@@ skipping 609 matching lines @@
 
 inline const Attribute* ElementData::attributeItem(unsigned index) const
 {
     RELEASE_ASSERT(index < length());
     return attributeBase() + index;
 }
 
 } // namespace
 
 #endif