Add message to Ash message center for no notifications

ash/system/web_notification/web_notification_tray.h

 // 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.
 
 #ifndef ASH_SYSTEM_NOTIFICATION_WEB_NOTIFICATION_TRAY_H_
 #define ASH_SYSTEM_NOTIFICATION_WEB_NOTIFICATION_TRAY_H_
 
 #include "ash/ash_export.h"
 #include "ash/system/tray/tray_background_view.h"
 #include "ash/system/user/login_status.h"
@@ skipping 92 matching lines @@
   // Disable all notifications matching notification |id|.
   void DisableByExtension(const std::string& id);
   void DisableByUrl(const std::string& id);
 
   // Show the message center bubble. Should only be called by StatusAreaWidget.
   void ShowMessageCenterBubble();
 
   // Hide the message center bubble. Should only be called by StatusAreaWidget.
   void HideMessageCenterBubble();
 
+  // Hide the message center bubble if there are no notifications.
+  void HideMessageCenterBubbleIfEmpty();
+
   // Show a single notification bubble for the most recent notification.
   void ShowNotificationBubble();
 
   // Hide the single notification bubble if visible.
   void HideNotificationBubble();
 
   // Updates tray visibility login status of the system changes.
   void UpdateAfterLoginStatusChange(user::LoginStatus login_status);
 
   // Request the Delegate to the settings dialog.
@@ skipping 29 matching lines @@
   views::Label* count_label_;
   Delegate* delegate_;
   bool show_message_center_on_unlock_;
 
   DISALLOW_COPY_AND_ASSIGN(WebNotificationTray);
 };
 
 }  // namespace ash
 
 #endif  // ASH_SYSTEM_NOTIFICATION_WEB_NOTIFICATION_TRAY_H_