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

Source/core/svg/SVGSwitchElement.h

Index: Source/core/svg/SVGSwitchElement.h
diff --git a/Source/core/svg/SVGSwitchElement.h b/Source/core/svg/SVGSwitchElement.h
index 0c4aa9ecab83d72555fe847bbe18f8a96780eea4..0749ddf3e679e551290b4540e28b7113148fefc9 100644
--- a/Source/core/svg/SVGSwitchElement.h
+++ b/Source/core/svg/SVGSwitchElement.h
@@ -38,6 +38,8 @@ class SVGSwitchElement : public SVGStyledTransformableElement,
 public:
     static PassRefPtr<SVGSwitchElement> create(const QualifiedName&, const Handle<Document>&);
 
+    virtual void accept(Visitor* visitor) const OVERRIDE { SVGStyledTransformableElement::accept(visitor); }
+
 private:
     SVGSwitchElement(const QualifiedName&, const Handle<Document>&);