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);
+    }
+
 private:
     short m_tabindex;