Oilpan: Make the Node hierarchy RefCountedGarbageCollected instead of TreeShared.

Source/core/dom/UserActionElementSet.cpp

Index: Source/core/dom/UserActionElementSet.cpp
diff --git a/Source/core/dom/UserActionElementSet.cpp b/Source/core/dom/UserActionElementSet.cpp
index 264061fd539b7220366ad1974aba8c9571c93064..e59d1fa6003c69af4516253d23b064c5baded77b 100644
--- a/Source/core/dom/UserActionElementSet.cpp
+++ b/Source/core/dom/UserActionElementSet.cpp
@@ -46,10 +46,12 @@ void UserActionElementSet::didDetach(Node* node)
     clearFlags(toElement(node), IsActiveFlag | InActiveChainFlag | IsHoveredFlag);
 }
 
+#if !ENABLE(OILPAN)
 void UserActionElementSet::documentDidRemoveLastRef()
 {
     m_elements.clear();
 }
+#endif
 
 bool UserActionElementSet::hasFlags(const Node* node, unsigned flags) const
 {
@@ -116,4 +118,9 @@ inline void UserActionElementSet::setFlags(Element* element, unsigned flags)
     m_elements.add(element, flags);
 }
 
+void UserActionElementSet::trace(Visitor* visitor)
+{
+    visitor->trace(m_elements);
+}
+
 }