Made --enable-rich-notifications flag available to message_center.

ui/message_center/message_center_switches.cc

 // Copyright (c) 2012 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 "ui/message_center/message_center_switches.h"
 
 namespace message_center {
 namespace switches {
 
 const char kDisableNewMessageCenterBubble[] =
     "disable-new-message-center-bubble";
 
+const char kEnableRichNotifications[] = "enable-rich-notifications";
+
+const char kEnableNewSimpleNotifications[] = "enable-new-simple-notifications";
+
 }  // namespace switches
 }  // namespace message_center