Implement contextmenu attribute with basic support of <menu>

Source/core/html/HTMLMenuitemElement.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#ifndef HTMLPictureElement_h
-#define HTMLPictureElement_h
+#ifndef HTMLMenuitemElement_h
+#define HTMLMenuitemElement_h
 
 #include "core/html/HTMLElement.h"
 
 namespace WebCore {
 
-class HTMLPictureElement FINAL : public HTMLElement {
+class HTMLMenuitemElement FINAL : public HTMLElement {
 public:
-    static PassRefPtr<HTMLPictureElement> create(Document&);
+    static PassRefPtr<HTMLMenuitemElement> create(Document&);
 
-protected:
-    explicit HTMLPictureElement(Document&);
+private:
+    explicit HTMLMenuitemElement(Document&);
 };
 
 } // namespace
 
 #endif