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

Source/core/svg/SVGPolylineElement.h

Index: Source/core/svg/SVGPolylineElement.h
diff --git a/Source/core/svg/SVGPolylineElement.h b/Source/core/svg/SVGPolylineElement.h
index e47623d2540b6d8bf5c9fe61a72c0a8813aabff1..8c65a221f472ce974b88f5221562b24c596ecdf6 100644
--- a/Source/core/svg/SVGPolylineElement.h
+++ b/Source/core/svg/SVGPolylineElement.h
@@ -30,6 +30,8 @@ class SVGPolylineElement : public SVGPolyElement {
 public:
     static PassRefPtr<SVGPolylineElement> create(const QualifiedName&, const Handle<Document>&);
 
+    virtual void accept(Visitor* visitor) const OVERRIDE { SVGPolyElement::accept(visitor); }
+
 private:
     SVGPolylineElement(const QualifiedName&, const Handle<Document>&);
 };