Implement contextmenu attribute with basic support of <menu>

Source/core/html/HTMLMenuItemElement.cpp

+// 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.
+
+#include "config.h"
+#include "core/html/HTMLMenuItemElement.h"
+
+#include "HTMLNames.h"
+
+namespace WebCore {
+
+using namespace HTMLNames;
+
+inline HTMLMenuItemElement::HTMLMenuItemElement(Document& document)
+    : HTMLElement(menuitemTag, document)
+{
+    ScriptWrappable::init(this);
+}
+
+PassRefPtr<HTMLMenuItemElement> HTMLMenuItemElement::create(Document& document)
+{
+    return adoptRef(new HTMLMenuItemElement(document));
+}
+
+}