[oilpan] Implement accept methods to trace the class hierarchy of SVGElement and all sub-classes.

Source/core/svg/SVGSetElement.h

Index: Source/core/svg/SVGSetElement.h
diff --git a/Source/core/svg/SVGSetElement.h b/Source/core/svg/SVGSetElement.h
index bed47f13cc0f40b240d24456de69140724f31db8..9cf630756450f8c55e4676076be168b3fe79c574 100644
--- a/Source/core/svg/SVGSetElement.h
+++ b/Source/core/svg/SVGSetElement.h
@@ -31,6 +31,8 @@ class SVGSetElement : public SVGAnimateElement {
 public:
     static PassRefPtr<SVGSetElement> create(const QualifiedName&, const Handle<Document>&);
 
+    virtual void accept(Visitor* visitor) const OVERRIDE { SVGAnimateElement::accept(visitor); }
+
 private:
     SVGSetElement(const QualifiedName&, const Handle<Document>&);
     virtual void updateAnimationMode() OVERRIDE;