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

Source/core/svg/SVGForeignObjectElement.h

Index: Source/core/svg/SVGForeignObjectElement.h
diff --git a/Source/core/svg/SVGForeignObjectElement.h b/Source/core/svg/SVGForeignObjectElement.h
index 84dcb4f805d2055ea12947497d4fb4092438b1c1..9ca710f0c45dfab7542fdeed3abc30306619ed2d 100644
--- a/Source/core/svg/SVGForeignObjectElement.h
+++ b/Source/core/svg/SVGForeignObjectElement.h
@@ -38,6 +38,8 @@ class SVGForeignObjectElement : public SVGStyledTransformableElement,
 public:
     static PassRefPtr<SVGForeignObjectElement> create(const QualifiedName&, const Handle<Document>&);
 
+    virtual void accept(Visitor* visitor) const OVERRIDE { SVGStyledTransformableElement::accept(visitor); }
+
 private:
     SVGForeignObjectElement(const QualifiedName&, const Handle<Document>&);