[oilpan] Completely move HTMLFormControlElement's hierarchy to the managed heap

Source/core/html/HTMLKeygenElement.h

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2000 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2010 Apple Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
@@ skipping 14 matching lines @@
 #define HTMLKeygenElement_h
 
 #include "core/html/HTMLFormControlElementWithState.h"
 
 namespace WebCore {
 
 class HTMLSelectElement;
 
 class HTMLKeygenElement : public HTMLFormControlElementWithState {
 public:
-    static PassRefPtr<HTMLKeygenElement> create(const QualifiedName&, Document*, HTMLFormElement*);
+    static Result<HTMLKeygenElement> create(const QualifiedName&, Document*, HTMLFormElement*);
 
     virtual bool willValidate() const { return false; }
 
+    virtual void acceptHeapVisitor(Visitor*) const OVERRIDE;
+
 private:
     HTMLKeygenElement(const QualifiedName&, Document*, HTMLFormElement*);
 
     virtual bool areAuthorShadowsAllowed() const OVERRIDE { return false; }
 
     virtual bool canStartSelection() const { return false; }
 
     virtual void parseAttribute(const QualifiedName&, const AtomicString&) OVERRIDE;
 
     virtual bool appendFormData(FormDataList&, bool);
     virtual const AtomicString& formControlType() const;
     virtual bool isOptionalFormControl() const { return false; }
 
     virtual bool isEnumeratable() const { return true; }
     virtual bool supportLabels() const OVERRIDE { return true; }
 
     virtual void reset();
     virtual bool shouldSaveAndRestoreFormControlState() const OVERRIDE;
 
-    HTMLSelectElement* shadowSelect() const;
+    Result<HTMLSelectElement> shadowSelect() const;
 };
 
 } //namespace
 
 #endif