Remove the OnError method from notification delegates.

ui/message_center/notification_delegate.cc

 // Copyright 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.
 
 #include "ui/message_center/notification_delegate.h"
 
 namespace message_center {
 
 // NotificationDelegate:
 
 void NotificationDelegate::Display() {}
 
-void NotificationDelegate::Error() {}
-
 void NotificationDelegate::Close(bool by_user) {}
 
 bool NotificationDelegate::HasClickedListener() { return false; }
 
 void NotificationDelegate::Click() {}
 
 void NotificationDelegate::ButtonClick(int button_index) {}
 
 // HandleNotificationClickedDelegate:
 
@@ skipping 22 matching lines @@
 
 HandleNotificationButtonClickDelegate::
     ~HandleNotificationButtonClickDelegate() {}
 
 void HandleNotificationButtonClickDelegate::ButtonClick(int button_index) {
   if (!button_callback_.is_null())
     button_callback_.Run(button_index);
 }
 
 }  // namespace message_center