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

Source/core/svg/SVGMissingGlyphElement.h

Index: Source/core/svg/SVGMissingGlyphElement.h
diff --git a/Source/core/svg/SVGMissingGlyphElement.h b/Source/core/svg/SVGMissingGlyphElement.h
index 31a0915645af82309dc065c3dabcfa10442d79e4..e9ad138a19e305c1a70b4dd532b990d491f3e8aa 100644
--- a/Source/core/svg/SVGMissingGlyphElement.h
+++ b/Source/core/svg/SVGMissingGlyphElement.h
@@ -29,6 +29,8 @@ class SVGMissingGlyphElement : public SVGStyledElement {
 public:
     static PassRefPtr<SVGMissingGlyphElement> create(const QualifiedName&, const Handle<Document>&);
 
+    virtual void accept(Visitor* visitor) const OVERRIDE { SVGStyledElement::accept(visitor); }
+
 private:
     SVGMissingGlyphElement(const QualifiedName&, const Handle<Document>&);