Use a direct include of strings headers in ui/, part 2.

ui/message_center/notification.h

 // Copyright (c) 2013 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 UI_MESSAGE_CENTER_NOTIFICATION_H_
 #define UI_MESSAGE_CENTER_NOTIFICATION_H_
 
 #include <string>
 #include <vector>
 
-#include "base/string16.h"
+#include "base/strings/string16.h"
 #include "base/time.h"
 #include "base/values.h"
 #include "ui/gfx/image/image.h"
 #include "ui/message_center/message_center_export.h"
 #include "ui/message_center/notification_delegate.h"
 #include "ui/message_center/notification_types.h"
 
 namespace message_center {
 
 struct MESSAGE_CENTER_EXPORT NotificationItem {
@@ skipping 156 matching lines @@
   bool is_expanded_;  // True if this has been expanded in the message center.
 
   // A proxy object that allows access back to the JavaScript object that
   // represents the notification, for firing events.
   scoped_refptr<NotificationDelegate> delegate_;
 };
 
 }  // namespace message_center
 
 #endif  // UI_MESSAGE_CENTER_NOTIFICATION_H_