Make CSSParserContext be garbage collected.

third_party/WebKit/Source/core/css/CSSRule.cpp

 /*
  * (C) 1999-2003 Lars Knoll (knoll@kde.org)
  * (C) 2002-2003 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2002, 2005, 2006, 2007, 2012 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
  * version 2 of the License, or (at your option) any later version.
  *
@@ skipping 20 matching lines @@
 struct SameSizeAsCSSRule : public GarbageCollectedFinalized<SameSizeAsCSSRule>,
                            public ScriptWrappable {
   virtual ~SameSizeAsCSSRule();
   unsigned char bitfields;
   void* pointerUnion;
 };
 
 static_assert(sizeof(CSSRule) == sizeof(SameSizeAsCSSRule),
               "CSSRule should stay small");
 
-const CSSParserContext& CSSRule::parserContext() const {
+const CSSParserContext* CSSRule::parserContext() const {
   CSSStyleSheet* styleSheet = parentStyleSheet();
   return styleSheet ? styleSheet->contents()->parserContext()
                     : strictCSSParserContext();
 }
 
 void CSSRule::setParentStyleSheet(CSSStyleSheet* styleSheet) {
   m_parentIsRule = false;
   m_parentStyleSheet = styleSheet;
   ScriptWrappableVisitor::writeBarrier(this, m_parentStyleSheet);
 }
 
 void CSSRule::setParentRule(CSSRule* rule) {
   m_parentIsRule = true;
   m_parentRule = rule;
   ScriptWrappableVisitor::writeBarrier(this, m_parentRule);
 }
 
 DEFINE_TRACE(CSSRule) {
   // This makes the parent link strong, which is different from the
   // pre-oilpan world, where the parent link is mysteriously zeroed under
   // some circumstances.
   if (m_parentIsRule)
     visitor->trace(m_parentRule);
   else
     visitor->trace(m_parentStyleSheet);
 }
 
 }  // namespace blink