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

Source/core/svg/SVGPathElement.h

Index: Source/core/svg/SVGPathElement.h
diff --git a/Source/core/svg/SVGPathElement.h b/Source/core/svg/SVGPathElement.h
index 2a80175e9636a547ad99c46a66bd905270e2364e..743efe306b1127cfb3a33c5ee199d572513b3f17 100644
--- a/Source/core/svg/SVGPathElement.h
+++ b/Source/core/svg/SVGPathElement.h
@@ -103,6 +103,8 @@ public:
 
     bool isAnimValObserved() const { return m_isAnimValObserved; }
 
+    virtual void accept(Visitor* visitor) const OVERRIDE { SVGStyledTransformableElement::accept(visitor); }
+
 private:
     SVGPathElement(const QualifiedName&, const Handle<Document>&);