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

Source/core/svg/SVGAElement.h

Index: Source/core/svg/SVGAElement.h
diff --git a/Source/core/svg/SVGAElement.h b/Source/core/svg/SVGAElement.h
index ff7b9c2d9847b91f255f3e91bb3db5c81bc18530..28fd8d711d3e9af3df5c9f58dffc9b16bff0a6c1 100644
--- a/Source/core/svg/SVGAElement.h
+++ b/Source/core/svg/SVGAElement.h
@@ -41,6 +41,8 @@ class SVGAElement : public SVGStyledTransformableElement,
 public:
     static PassRefPtr<SVGAElement> create(const QualifiedName&, const Handle<Document>&);
 
+    virtual void accept(Visitor* visitor) const OVERRIDE { SVGStyledTransformableElement::accept(visitor); }
+
 private:
     SVGAElement(const QualifiedName&, const Handle<Document>&);