Implement contextmenu attribute with basic support of <menu>

Source/core/html/HTMLMenuItemElement.idl

Index: Source/core/html/HTMLMenuItemElement.idl
diff --git a/Source/core/html/HTMLMenuItemElement.idl b/Source/core/html/HTMLMenuItemElement.idl
new file mode 100644
index 0000000000000000000000000000000000000000..8c148b6bd36158cce345f8b8cb8b8b3bf239386a
--- /dev/null
+++ b/Source/core/html/HTMLMenuItemElement.idl
@@ -0,0 +1,14 @@
+// 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.
+
+[
+    RuntimeEnabled=ContextMenu,
+] interface HTMLMenuItemElement : HTMLElement {
+    [Reflect] attribute DOMString type;
+    [Reflect] attribute DOMString label;
+    [Reflect] attribute boolean disabled;
+    [Reflect] attribute boolean checked;
+    [Reflect] attribute boolean default;
+    // FIXME(sanjoy): icon, radiogroup and command need to be implemented. 
+};