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

Source/core/svg/SVGEllipseElement.h

Index: Source/core/svg/SVGEllipseElement.h
diff --git a/Source/core/svg/SVGEllipseElement.h b/Source/core/svg/SVGEllipseElement.h
index 1f499100f4253d65079fb59a7bb0250c1fb3bcf8..82fd39de0caa0e31381d2a466f1059befe3dc718 100644
--- a/Source/core/svg/SVGEllipseElement.h
+++ b/Source/core/svg/SVGEllipseElement.h
@@ -39,6 +39,8 @@ class SVGEllipseElement : public SVGStyledTransformableElement,
 public:
     static PassRefPtr<SVGEllipseElement> create(const QualifiedName&, const Handle<Document>&);
 
+    virtual void accept(Visitor* visitor) const OVERRIDE { SVGStyledTransformableElement::accept(visitor); }
+
 private:
     SVGEllipseElement(const QualifiedName&, const Handle<Document>&);