Move StyleSheet to the oilpan heap using transition types.

Source/core/css/StyleSheet.h

 /*
  * (C) 1999-2003 Lars Knoll (knoll@kde.org)
  * Copyright (C) 2004, 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.
  *
  * This library is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  * Library General Public License for more details.
  *
  * You should have received a copy of the GNU Library General Public License
  * along with this library; see the file COPYING.LIB.  If not, write to
  * the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
  * Boston, MA 02110-1301, USA.
  */
 
 #ifndef StyleSheet_h
 #define StyleSheet_h
 
 #include "core/css/CSSParserMode.h"
+#include "heap/Handle.h"
 #include "wtf/Forward.h"
 #include "wtf/RefCounted.h"
 
 namespace WebCore {
 
 class CSSRule;
 class KURL;
 class MediaList;
 class Node;
 class StyleSheet;
 
-class StyleSheet : public RefCounted<StyleSheet> {
+class StyleSheet : public RefCountedWillBeRefCountedGarbageCollected<StyleSheet> {
 public:
     virtual ~StyleSheet();
 
     virtual bool disabled() const = 0;
     virtual void setDisabled(bool) = 0;
     virtual Node* ownerNode() const = 0;
     virtual StyleSheet* parentStyleSheet() const { return 0; }
     virtual String href() const = 0;
     virtual String title() const = 0;
     virtual MediaList* media() const { return 0; }
     virtual String type() const = 0;
 
     virtual CSSRule* ownerRule() const { return 0; }
     virtual void clearOwnerNode() = 0;
     virtual KURL baseURL() const = 0;
     virtual bool isLoading() const = 0;
     virtual bool isCSSStyleSheet() const { return false; }
+
+    virtual void trace(Visitor*) = 0;
 };
 
 } // namespace
 
 #endif