Make CSSParserContext be garbage collected.

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

 /*
  * (C) 1999-2003 Lars Knoll (knoll@kde.org)
  * (C) 2002-2003 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2002, 2005, 2006, 2008, 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 59 matching lines @@
   }
 
   ASSERT(!selectorTextCache().contains(this));
   String text = generateSelectorText();
   selectorTextCache().set(this, text);
   setHasCachedSelectorText(true);
   return text;
 }
 
 void CSSStyleRule::setSelectorText(const String& selectorText) {
-  CSSParserContext context(parserContext(), nullptr);
+  const CSSParserContext* context =
+      CSSParserContext::create(parserContext(), nullptr);
   CSSSelectorList selectorList = CSSParser::parseSelector(
       context, parentStyleSheet() ? parentStyleSheet()->contents() : nullptr,
       selectorText);
   if (!selectorList.isValid())
     return;
 
   CSSStyleSheet::RuleMutationScope mutationScope(this);
 
   m_styleRule->wrapperAdoptSelectorList(std::move(selectorList));
 
@@ skipping 28 matching lines @@
   CSSRule::trace(visitor);
 }
 
 DEFINE_TRACE_WRAPPERS(CSSStyleRule) {
   visitor->traceWrappers(parentRule());
   visitor->traceWrappers(parentStyleSheet());
   CSSRule::traceWrappers(visitor);
 }
 
 }  // namespace blink