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

Source/core/svg/SVGFEDisplacementMapElement.h

Index: Source/core/svg/SVGFEDisplacementMapElement.h
diff --git a/Source/core/svg/SVGFEDisplacementMapElement.h b/Source/core/svg/SVGFEDisplacementMapElement.h
index 082364072f4546a0a712c9d093a9797c677976af..a2c349af55abf92362c2f0a1d75a3e4b29709a32 100644
--- a/Source/core/svg/SVGFEDisplacementMapElement.h
+++ b/Source/core/svg/SVGFEDisplacementMapElement.h
@@ -70,7 +70,9 @@ public:
     static PassRefPtr<SVGFEDisplacementMapElement> create(const QualifiedName&, const Handle<Document>&);
 
     static ChannelSelectorType stringToChannel(const String&);
-    
+
+    virtual void accept(Visitor* visitor) const OVERRIDE { SVGFilterPrimitiveStandardAttributes::accept(visitor); }
+
 private:
     SVGFEDisplacementMapElement(const QualifiedName& tagName, const Handle<Document>&);