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

Source/core/svg/SVGFEMergeElement.h

Index: Source/core/svg/SVGFEMergeElement.h
diff --git a/Source/core/svg/SVGFEMergeElement.h b/Source/core/svg/SVGFEMergeElement.h
index e2b766504c63b602cf51cf94ae45b1dda0089342..0b118c07f6a54afdb33fdee8c2dca29fe09b8301 100644
--- a/Source/core/svg/SVGFEMergeElement.h
+++ b/Source/core/svg/SVGFEMergeElement.h
@@ -31,6 +31,8 @@ class SVGFEMergeElement : public SVGFilterPrimitiveStandardAttributes {
 public:
     static PassRefPtr<SVGFEMergeElement> create(const QualifiedName&, const Handle<Document>&);
 
+    virtual void accept(Visitor* visitor) const OVERRIDE { SVGFilterPrimitiveStandardAttributes::accept(visitor); }
+
 private:
     SVGFEMergeElement(const QualifiedName&, const Handle<Document>&);