Remove the OnError method from notification delegates.

ui/message_center/notification_delegate.h

 // 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.
 
 #ifndef UI_MESSAGE_CENTER_NOTIFICATION_DELEGATE_H_
 #define UI_MESSAGE_CENTER_NOTIFICATION_DELEGATE_H_
 
 #include <string>
 
 #include "base/callback.h"
 #include "base/memory/ref_counted.h"
 #include "ui/message_center/message_center_export.h"
 
 namespace content {
 class RenderViewHost;
 }
 
 namespace message_center {
 
 // Delegate for a notification. This class has two roles: to implement callback
 // methods for notification, and to provide an identity of the associated
 // notification.
 class MESSAGE_CENTER_EXPORT NotificationDelegate
     : public base::RefCountedThreadSafe<NotificationDelegate> {
  public:
   // To be called when the desktop notification is actually shown.
   virtual void Display();
 
-  // To be called when the desktop notification cannot be shown due to an
-  // error.
-  virtual void Error();
-
   // To be called when the desktop notification is closed.  If closed by a
   // user explicitly (as opposed to timeout/script), |by_user| should be true.
   virtual void Close(bool by_user);
 
   // Returns true if the delegate can handle click event.
   virtual bool HasClickedListener();
 
   // To be called when a desktop notification is clicked.
   virtual void Click();
 
@@ skipping 45 matching lines @@
 
  private:
   ButtonClickCallback button_callback_;
 
   DISALLOW_COPY_AND_ASSIGN(HandleNotificationButtonClickDelegate);
 };
 
 }  //  namespace message_center
 
 #endif  // UI_MESSAGE_CENTER_NOTIFICATION_DELEGATE_H_