Move StyleSheet to the oilpan heap using transition types.

Source/core/css/CSSRule.h

 /*
  * (C) 1999-2003 Lars Knoll (knoll@kde.org)
  * (C) 2002-2003 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2002, 2006, 2007, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2011 Andreas Kling (kling@webkit.org)
  *
  * 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 90 matching lines @@
 
     bool hasCachedSelectorText() const { return m_hasCachedSelectorText; }
     void setHasCachedSelectorText(bool hasCachedSelectorText) const { m_hasCachedSelectorText = hasCachedSelectorText; }
 
     const CSSParserContext& parserContext() const;
 
 private:
     mutable unsigned char m_hasCachedSelectorText : 1;
     unsigned char m_parentIsRule : 1;
 
+    // These should be Members, but no Members in unions.
     union {
-        CSSRule* m_parentRule; // Should be Member, but no Members in unions.
+        CSSRule* m_parentRule;
         CSSStyleSheet* m_parentStyleSheet;
     };
 };
 
 #define DEFINE_CSS_RULE_TYPE_CASTS(ToType, TYPE_NAME) \
     DEFINE_TYPE_CASTS(ToType, CSSRule, rule, rule->type() == CSSRule::TYPE_NAME, rule.type() == CSSRule::TYPE_NAME)
 
 } // namespace WebCore
 
 #endif // CSSRule_h