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

Source/core/svg/SVGRectElement.h

Index: Source/core/svg/SVGRectElement.h
diff --git a/Source/core/svg/SVGRectElement.h b/Source/core/svg/SVGRectElement.h
index 6a15eb446263238c11c1dc120ecc9fe00404f40c..1a745906bde4ef907713d879ea3cf4bd926132a0 100644
--- a/Source/core/svg/SVGRectElement.h
+++ b/Source/core/svg/SVGRectElement.h
@@ -39,6 +39,8 @@ class SVGRectElement : public SVGStyledTransformableElement,
 public:
     static PassRefPtr<SVGRectElement> create(const QualifiedName&, const Handle<Document>&);
 
+    virtual void accept(Visitor* visitor) const OVERRIDE { SVGStyledTransformableElement::accept(visitor); }
+
 private:
     SVGRectElement(const QualifiedName&, const Handle<Document>&);