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

Source/core/svg/SVGFEDropShadowElement.h

Index: Source/core/svg/SVGFEDropShadowElement.h
diff --git a/Source/core/svg/SVGFEDropShadowElement.h b/Source/core/svg/SVGFEDropShadowElement.h
index 42c2e09a5ac6106ff63c0c75984f15e9bd932b91..575789aacb5caae49258190c16a63ebc56560b0b 100644
--- a/Source/core/svg/SVGFEDropShadowElement.h
+++ b/Source/core/svg/SVGFEDropShadowElement.h
@@ -32,7 +32,9 @@ public:
     static PassRefPtr<SVGFEDropShadowElement> create(const QualifiedName&, const Handle<Document>&);
     
     void setStdDeviation(float stdDeviationX, float stdDeviationY);
-    
+
+    virtual void accept(Visitor* visitor) const OVERRIDE { SVGFilterPrimitiveStandardAttributes::accept(visitor); }
+
 private:
     SVGFEDropShadowElement(const QualifiedName&, const Handle<Document>&);