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

Source/core/svg/SVGLineElement.h

Index: Source/core/svg/SVGLineElement.h
diff --git a/Source/core/svg/SVGLineElement.h b/Source/core/svg/SVGLineElement.h
index 8a805ddce4aeb0e5bccd72bded9fe970bce9e51b..81e3c80f1800290e719ed083722d7ba83e1328f1 100644
--- a/Source/core/svg/SVGLineElement.h
+++ b/Source/core/svg/SVGLineElement.h
@@ -38,6 +38,8 @@ class SVGLineElement : public SVGStyledTransformableElement,
 public:
     static PassRefPtr<SVGLineElement> create(const QualifiedName&, const Handle<Document>&);
 
+    virtual void accept(Visitor* visitor) const OVERRIDE { SVGStyledTransformableElement::accept(visitor); }
+
 private:
     SVGLineElement(const QualifiedName&, const Handle<Document>&);