Oilpan: Make the Node hierarchy RefCountedGarbageCollected instead of TreeShared.

Source/core/dom/ElementRareData.h

Index: Source/core/dom/ElementRareData.h
diff --git a/Source/core/dom/ElementRareData.h b/Source/core/dom/ElementRareData.h
index ce94cc2a281382ed8d71ecd8f9aa741edc24c1c5..c3419e84a66503b765a8c6f16a53584c67558cd5 100644
--- a/Source/core/dom/ElementRareData.h
+++ b/Source/core/dom/ElementRareData.h
@@ -119,6 +119,16 @@ public:
     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;