Have Document::elementSheet() return a reference

Source/core/css/PropertySetCSSStyleDeclaration.cpp

 /*
  * (C) 1999-2003 Lars Knoll (knoll@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2011 Research In Motion Limited. 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
  * version 2 of the License, or (at your option) any later version.
  *
@@ skipping 365 matching lines @@
         return;
 
     m_parentElement->clearMutableInlineStyleIfEmpty();
     m_parentElement->setNeedsStyleRecalc(LocalStyleChange);
     m_parentElement->invalidateStyleAttribute();
     StyleAttributeMutationScope(this).didInvalidateStyleAttr();
 }
 
 CSSStyleSheet* InlineCSSStyleDeclaration::parentStyleSheet() const
 {
-    return m_parentElement ? m_parentElement->document().elementSheet() : 0;
+    return m_parentElement ? &m_parentElement->document().elementSheet() : 0;
 }
 
 void InlineCSSStyleDeclaration::ref()
 {
     m_parentElement->ref();
 }
 
 void InlineCSSStyleDeclaration::deref()
 {
     m_parentElement->deref();
 }
 
 } // namespace WebCore