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

Source/core/svg/SVGTextElement.h

Index: Source/core/svg/SVGTextElement.h
diff --git a/Source/core/svg/SVGTextElement.h b/Source/core/svg/SVGTextElement.h
index 19d68faa17214295d19dec0cfaeebe93aa38f06a..3ce41ee671b3be6cb4e43acc0ed33a2dd264f3fb 100644
--- a/Source/core/svg/SVGTextElement.h
+++ b/Source/core/svg/SVGTextElement.h
@@ -41,6 +41,8 @@ public:
     virtual AffineTransform getScreenCTM(StyleUpdateStrategy = AllowStyleUpdate);
     virtual AffineTransform animatedLocalTransform() const;
 
+    virtual void accept(Visitor* visitor) const OVERRIDE { SVGTextPositioningElement::accept(visitor); }
+
 private:
     SVGTextElement(const QualifiedName&, const Handle<Document>&);