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

Source/core/svg/SVGTextPathElement.h

Index: Source/core/svg/SVGTextPathElement.h
diff --git a/Source/core/svg/SVGTextPathElement.h b/Source/core/svg/SVGTextPathElement.h
index 20e91be0f6a6c9ec66a9680df2c94aa88062eede..8c72f096b4f6898fa7a16bb14a995e13ecf81c3d 100644
--- a/Source/core/svg/SVGTextPathElement.h
+++ b/Source/core/svg/SVGTextPathElement.h
@@ -112,7 +112,9 @@ public:
     };
 
     static PassRefPtr<SVGTextPathElement> create(const QualifiedName&, const Handle<Document>&);
- 
+
+    virtual void accept(Visitor* visitor) const OVERRIDE { SVGTextContentElement::accept(visitor); }
+
 private:
     SVGTextPathElement(const QualifiedName&, const Handle<Document>&);