Oilpan: Make the Node hierarchy RefCountedGarbageCollected instead of TreeShared.

Source/core/dom/ElementRareData.h

 /*
  * Copyright (C) 2008, 2009, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2008 David Smith <catfish.man@gmail.com>
  *
  * 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 101 matching lines @@
             m_inputMethodContext = InputMethodContext::create(element);
         return *m_inputMethodContext;
     }
 
     bool hasPseudoElements() const;
     void clearPseudoElements();
 
     void setCustomElementDefinition(PassRefPtr<CustomElementDefinition> definition) { m_customElementDefinition = definition; }
     CustomElementDefinition* customElementDefinition() const { return m_customElementDefinition.get(); }
 
+    void trace(Visitor* visitor)
+    {
+        // FIXME: Oilpan: Implement real tracing of the
+        // ElementRareData when it has been moved to the
+        // oilpan heap and move the ElementShadow tracing
+        // to the ElementShadow when that has been moved
+        // to the oilpan heap.
+        visitor->trace(m_shadow);

[haraken, 2014/05/06 04:20:16]

It's confusing that ElementShadow is traced but ElementRareData::m_shadow is
kept as an OwnPtr. Can we move ElementShadow to the heap at the same time in
this CL? (I guess you already implemented ElementShadow::trace() in this CL, so
it won't that hard to change ElementShadow to
NoBaseWillBeGarbageCollectedFinalized.)

[Mads Ager (chromium), 2014/05/06 08:26:00]

I would prefer to do that as a followup. Moving more to the oilpan heap in this
change can lead to more finalization order issues. We need this to land soon so
it is safe to replace RefPtr with Member to the Node hierarchy.

+    }
+
 private:
     short m_tabindex;
 
     IntSize m_savedLayerScrollOffset;
 
     OwnPtr<DatasetDOMStringMap> m_dataset;
     OwnPtr<ClassList> m_classList;
     OwnPtr<ElementShadow> m_shadow;
     OwnPtr<NamedNodeMap> m_attributeMap;
     OwnPtr<InputMethodContext> m_inputMethodContext;
@@ skipping 74 matching lines @@
 }
 
 inline void ElementRareData::resetStyleState()
 {
     clearElementFlag(StyleAffectedByEmpty);
 }
 
 } // namespace
 
 #endif // ElementRareData_h