Oilpan: Make the Node hierarchy RefCountedGarbageCollected instead of TreeShared.

Source/core/dom/Element.cpp

Index: Source/core/dom/Element.cpp
diff --git a/Source/core/dom/Element.cpp b/Source/core/dom/Element.cpp
index cb9a9b0d3aca2ab7f11fc3432fada9ef947a9e92..2dfd3d91defb86c417803b23c919b68135a85f40 100644
--- a/Source/core/dom/Element.cpp
+++ b/Source/core/dom/Element.cpp
@@ -3295,4 +3295,13 @@ bool Element::supportsStyleSharing() const
     return true;
 }
 
+void Element::trace(Visitor* visitor)
+{
+    // FIXME: Oilpan: Perform this tracing directly on the element
+    // rare data once that is in the heap.
+    if (hasRareData())
+        elementRareData()->trace(visitor);
+    ContainerNode::trace(visitor);
+}
+
 } // namespace WebCore