Implement contextmenu attribute with basic support of <menu>

Source/core/html/HTMLMenuitemElement.h

Index: Source/core/html/HTMLMenuitemElement.h
diff --git a/Source/core/html/HTMLMenuitemElement.h b/Source/core/html/HTMLMenuitemElement.h
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+/*
+ * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
+ *           (C) 1999 Antti Koivisto (koivisto@kde.org)
+ * Copyright (C) 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.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Library General Public License for more details.
+ *
+ * You should have received a copy of the GNU Library General Public License
+ * along with this library; see the file COPYING.LIB.  If not, write to
+ * the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
+ * Boston, MA 02110-1301, USA.
+ *
+ */
+
+#ifndef HTMLMenuitemElement_h
+#define HTMLMenuitemElement_h
+
+#include "core/html/HTMLElement.h"
+
+namespace WebCore {
+
+class HTMLMenuitemElement FINAL : public HTMLElement {
+public:
+    static PassRefPtr<HTMLMenuitemElement> create(Document&);
+
+private:
+    explicit HTMLMenuitemElement(Document&);
+};
+
+} // namespace
+
+#endif