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

Source/core/svg/SVGStyledElement.h

Index: Source/core/svg/SVGStyledElement.h
diff --git a/Source/core/svg/SVGStyledElement.h b/Source/core/svg/SVGStyledElement.h
index 72b6d9285ed5c59b8896d394970452d0c52946fb..776cd7b36a311c9fc8e1ea68e5dea06bf148c3de 100644
--- a/Source/core/svg/SVGStyledElement.h
+++ b/Source/core/svg/SVGStyledElement.h
@@ -60,6 +60,8 @@ public:
     virtual Result<CSSStyleDeclaration> style() { return StyledElement::style(); }
     virtual bool needsPendingResourceHandling() const { return true; }
 
+    virtual void accept(Visitor* visitor) const OVERRIDE { SVGElement::accept(visitor); }
+
 protected: 
     SVGStyledElement(const QualifiedName&, const Handle<Document>&, ConstructionType = CreateSVGElement);
     virtual bool rendererIsNeeded(const NodeRenderingContext&);