Oilpan: Make the Node hierarchy RefCountedGarbageCollected instead of TreeShared.

Source/core/css/resolver/ElementResolveContext.h

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  * Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011 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,
@@ skipping 19 matching lines @@
 
 class ContainerNode;
 class Element;
 class RenderStyle;
 
 // ElementResolveContext is immutable and serves as an input to the style resolve process.
 class ElementResolveContext {
     STACK_ALLOCATED();
 public:
     ElementResolveContext()
-        : m_element(0)
-        , m_parentNode(0)
+        : m_element(nullptr)
+        , m_parentNode(nullptr)
         , m_rootElementStyle(0)
         , m_elementLinkState(NotInsideLink)
         , m_distributedToInsertionPoint(false)
     {
     }
 
     explicit ElementResolveContext(Element&);
 
     Element* element() const { return m_element; }
     const ContainerNode* parentNode() const { return m_parentNode; }
     const RenderStyle* rootElementStyle() const { return m_rootElementStyle; }
     EInsideLink elementLinkState() const { return m_elementLinkState; }
     bool distributedToInsertionPoint() const { return m_distributedToInsertionPoint; }
 
 private:
-    Element* m_element;
-    ContainerNode* m_parentNode;
+    RawPtrWillBeMember<Element> m_element;
+    RawPtrWillBeMember<ContainerNode> m_parentNode;
     RenderStyle* m_rootElementStyle;
     EInsideLink m_elementLinkState;
     bool m_distributedToInsertionPoint;
 };
 
 } // namespace WebCore
 
 #endif // ElementResolveContext_h