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

Source/core/svg/SVGTSpanElement.h

Index: Source/core/svg/SVGTSpanElement.h
diff --git a/Source/core/svg/SVGTSpanElement.h b/Source/core/svg/SVGTSpanElement.h
index be172eac146a62849cf94809f3a1b28e889f61d6..4729b6ae5b2d9bc1ae640323a9c3c5c7c529aa10 100644
--- a/Source/core/svg/SVGTSpanElement.h
+++ b/Source/core/svg/SVGTSpanElement.h
@@ -31,6 +31,8 @@ class SVGTSpanElement : public SVGTextPositioningElement {
 public:
     static PassRefPtr<SVGTSpanElement> create(const QualifiedName&, const Handle<Document>&);
 
+    virtual void accept(Visitor* visitor) const OVERRIDE { SVGTextPositioningElement::accept(visitor); }
+
 private:
     SVGTSpanElement(const QualifiedName&, const Handle<Document>&);