Oilpan: Prepare to move RenderObject and RenderObjectChildList to Oilpan heap.

Source/core/rendering/RenderListMarker.h

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  * Copyright (C) 2003, 2004, 2005, 2006, 2007, 2009 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 @@
 
 String listMarkerText(EListStyleType, int value);
 
 // Used to render the list item's marker.
 // The RenderListMarker always has to be a child of a RenderListItem.
 class RenderListMarker FINAL : public RenderBox {
 public:
     static RenderListMarker* createAnonymous(RenderListItem*);
 
     virtual ~RenderListMarker();
+    virtual void trace(Visitor*) OVERRIDE;
 
     const String& text() const { return m_text; }
     String suffix() const;
 
     bool isInside() const;
 
     void updateMarginsAndContent();
 
 private:
     RenderListMarker(RenderListItem*);
@@ skipping 25 matching lines @@
     void updateContent();
 
     virtual void styleWillChange(StyleDifference, const RenderStyle& newStyle) OVERRIDE;
     virtual void styleDidChange(StyleDifference, const RenderStyle* oldStyle) OVERRIDE;
 
     IntRect getRelativeMarkerRect();
     LayoutRect localSelectionRect();
 
     String m_text;
     RefPtr<StyleImage> m_image;
-    RenderListItem* m_listItem;
+    RawPtrWillBeMember<RenderListItem> m_listItem;
 };
 
 DEFINE_RENDER_OBJECT_TYPE_CASTS(RenderListMarker, isListMarker());
 
 } // namespace blink
 
 #endif // RenderListMarker_h