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

Source/core/svg/SVGImageElement.h

Index: Source/core/svg/SVGImageElement.h
diff --git a/Source/core/svg/SVGImageElement.h b/Source/core/svg/SVGImageElement.h
index 19a26da424b7ccc9de3c3a769744f53ec48863e0..fd2a366363cd0cf1350b68cd119281b3d88e3a2e 100644
--- a/Source/core/svg/SVGImageElement.h
+++ b/Source/core/svg/SVGImageElement.h
@@ -43,6 +43,8 @@ class SVGImageElement : public SVGStyledTransformableElement,
 public:
     static PassRefPtr<SVGImageElement> create(const QualifiedName&, const Handle<Document>&);
 
+    virtual void accept(Visitor* visitor) const OVERRIDE { SVGStyledTransformableElement::accept(visitor); }
+
 private:
     SVGImageElement(const QualifiedName&, const Handle<Document>&);