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

Source/core/svg/SVGFontFaceSrcElement.h

Index: Source/core/svg/SVGFontFaceSrcElement.h
diff --git a/Source/core/svg/SVGFontFaceSrcElement.h b/Source/core/svg/SVGFontFaceSrcElement.h
index 37d27d198be8f12157fdc3947cb6b694b3d148e5..32288f37f7c3d19755f63c5e288935d13ecbf82a 100644
--- a/Source/core/svg/SVGFontFaceSrcElement.h
+++ b/Source/core/svg/SVGFontFaceSrcElement.h
@@ -32,7 +32,9 @@ public:
     static PassRefPtr<SVGFontFaceSrcElement> create(const QualifiedName&, const Handle<Document>&);
 
     Result<CSSValueList> srcValue() const;
-    
+
+    virtual void accept(Visitor* visitor) const OVERRIDE { SVGElement::accept(visitor); }
+
 private:
     SVGFontFaceSrcElement(const QualifiedName&, const Handle<Document>&);