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

Source/core/html/HTMLUnknownElement.h

 /*
  * Copyright (c) 2011 Code Aurora Forum. 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
  *       copyright notice, this list of conditions and the following
@@ skipping 25 matching lines @@
 
 class HTMLUnknownElement : public HTMLElement {
 public:
     static PassRefPtr<HTMLUnknownElement> create(const QualifiedName& tagName, Handle<Document> document)
     {
         return adoptRef(new HTMLUnknownElement(tagName, document));
     }
 
     virtual bool isHTMLUnknownElement() const OVERRIDE { return true; }
 
+    virtual void acceptHeapVisitor(Visitor* visitor) const OVERRIDE
+    {
+        HTMLElement::acceptHeapVisitor(visitor);
+    }
+
 private:
     HTMLUnknownElement(const QualifiedName& tagName, Handle<Document> document)
         : HTMLElement(tagName, document)
     {
         ScriptWrappable::init(this);
     }
 };
 
 inline HTMLUnknownElement* toHTMLUnknownElement(HTMLElement* element)
 {
     ASSERT_WITH_SECURITY_IMPLICATION(!element || element->isHTMLUnknownElement());
     return static_cast<HTMLUnknownElement*>(element);
 }
 
 } // namespace
 
 #endif