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

Source/core/svg/SVGGElement.h

Index: Source/core/svg/SVGGElement.h
diff --git a/Source/core/svg/SVGGElement.h b/Source/core/svg/SVGGElement.h
index 546170a1a4d3ed04f1bb6431ada560620fcd4c8b..50a07269b56a7791623339bef2cf609ab7712838 100644
--- a/Source/core/svg/SVGGElement.h
+++ b/Source/core/svg/SVGGElement.h
@@ -38,6 +38,8 @@ class SVGGElement : public SVGStyledTransformableElement,
 public:
     static PassRefPtr<SVGGElement> create(const QualifiedName&, const Handle<Document>&);
 
+    virtual void accept(Visitor* visitor) const OVERRIDE { SVGStyledTransformableElement::accept(visitor); }
+
 protected:
     SVGGElement(const QualifiedName&, const Handle<Document>&, ConstructionType = CreateSVGElement);