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

Source/core/svg/SVGFEOffsetElement.h

Index: Source/core/svg/SVGFEOffsetElement.h
diff --git a/Source/core/svg/SVGFEOffsetElement.h b/Source/core/svg/SVGFEOffsetElement.h
index e422a97b03735c7617af2543fe2e42af6e9ce838..9ce85cf3de6c57f840163fd92dc16c4a41cab830 100644
--- a/Source/core/svg/SVGFEOffsetElement.h
+++ b/Source/core/svg/SVGFEOffsetElement.h
@@ -32,6 +32,8 @@ class SVGFEOffsetElement : public SVGFilterPrimitiveStandardAttributes {
 public:
     static PassRefPtr<SVGFEOffsetElement> create(const QualifiedName&, const Handle<Document>&);
 
+    virtual void accept(Visitor* visitor) const OVERRIDE { SVGFilterPrimitiveStandardAttributes::accept(visitor); }
+
 private:
     SVGFEOffsetElement(const QualifiedName&, const Handle<Document>&);