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
new file mode 100644
index 0000000000000000000000000000000000000000..19c7705e958f568308e94992ca106492ac92063b
--- /dev/null
+++ b/Source/core/html/HTMLMenuitemElement.h
@@ -0,0 +1,22 @@
+// 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 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