Oilpan: Replace RefPtr<Node> in core/svg/ with Oilpan transition types.

Source/core/svg/SVGFilterElement.h

Index: Source/core/svg/SVGFilterElement.h
diff --git a/Source/core/svg/SVGFilterElement.h b/Source/core/svg/SVGFilterElement.h
index 8b4e0a200128452a38305200104df2a9b982d4ff..a8479ed47542efe554c0cb105e83433fe263b6df 100644
--- a/Source/core/svg/SVGFilterElement.h
+++ b/Source/core/svg/SVGFilterElement.h
@@ -39,6 +39,7 @@ class SVGFilterElement FINAL : public SVGElement,
                                public SVGURIReference {
 public:
     DEFINE_NODE_FACTORY(SVGFilterElement);
+    virtual void trace(Visitor*) OVERRIDE;
 
     void setFilterRes(unsigned x, unsigned y);
     void addClient(Node*);
@@ -75,7 +76,7 @@ private:
     RefPtr<SVGAnimatedEnumeration<SVGUnitTypes::SVGUnitType> > m_primitiveUnits;
     RefPtr<SVGAnimatedIntegerOptionalInteger> m_filterRes;
 
-    HashSet<RefPtr<Node> > m_clientsToAdd;
+    WillBeHeapHashSet<RefPtrWillBeMember<Node> > m_clientsToAdd;
 };
 
 }