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

Source/core/svg/SVGFontFaceFormatElement.h

Index: Source/core/svg/SVGFontFaceFormatElement.h
diff --git a/Source/core/svg/SVGFontFaceFormatElement.h b/Source/core/svg/SVGFontFaceFormatElement.h
index e0d17a7aff507694cb74d836a438625044b3101c..bb0700a948224bb0f69cb05724615020304f2e78 100644
--- a/Source/core/svg/SVGFontFaceFormatElement.h
+++ b/Source/core/svg/SVGFontFaceFormatElement.h
@@ -29,6 +29,8 @@ class SVGFontFaceFormatElement : public SVGElement {
 public:
     static PassRefPtr<SVGFontFaceFormatElement> create(const QualifiedName&, const Handle<Document>&);
 
+    virtual void accept(Visitor* visitor) const OVERRIDE { SVGElement::accept(visitor); }
+
 private:
     SVGFontFaceFormatElement(const QualifiedName&, const Handle<Document>&);