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

Source/core/svg/SVGFEMergeNodeElement.h

Index: Source/core/svg/SVGFEMergeNodeElement.h
diff --git a/Source/core/svg/SVGFEMergeNodeElement.h b/Source/core/svg/SVGFEMergeNodeElement.h
index ad3ac664cdd9f83600bbf2fa6166be651142f847..30fffd0f37d95df04ce5f3a10e2214d038d8a884 100644
--- a/Source/core/svg/SVGFEMergeNodeElement.h
+++ b/Source/core/svg/SVGFEMergeNodeElement.h
@@ -31,6 +31,8 @@ class SVGFEMergeNodeElement : public SVGElement {
 public:
     static PassRefPtr<SVGFEMergeNodeElement> create(const QualifiedName&, const Handle<Document>&);
 
+    virtual void accept(Visitor* visitor) const OVERRIDE { SVGElement::accept(visitor); }
+
 private:
     SVGFEMergeNodeElement(const QualifiedName&, const Handle<Document>&);