[oilpan] The Node hierarchy should have correct accept method chains

Source/core/html/LabelableElement.h

 /*
  * Copyright (C) 2012 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 28 matching lines @@
 // specification, and provides the implementation of the "labels" attribute.
 class LabelableElement : public HTMLElement {
 public:
     virtual ~LabelableElement();
     PassRefPtr<NodeList> labels();
     virtual bool supportLabels() const { return false; }
 
 protected:
     LabelableElement(const QualifiedName& tagName, Handle<Document>);
 
+    virtual void acceptHeapVisitor(Visitor*) const OVERRIDE;
+
 private:
     virtual bool isLabelable() const OVERRIDE FINAL { return true; }
 };
 
 } // namespace WebCore
 
 #endif