Remove the OnError method from notification delegates.

chrome/browser/notifications/notification_object_proxy.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 CHROME_BROWSER_NOTIFICATIONS_NOTIFICATION_OBJECT_PROXY_H_
 #define CHROME_BROWSER_NOTIFICATIONS_NOTIFICATION_OBJECT_PROXY_H_
 
 #include <string>
 
 #include "base/memory/scoped_ptr.h"
 #include "chrome/browser/notifications/notification_delegate.h"
 
 namespace content {
 class DesktopNotificationDelegate;
 }
 
 // A NotificationObjectProxy stands in for the JavaScript Notification object
 // which corresponds to a notification toast on the desktop.  It can be signaled
 // when various events occur regarding the desktop notification, and the
 // attached JS listeners will be invoked in the renderer or worker process.
 class NotificationObjectProxy : public NotificationDelegate {
  public:
   // Creates a Proxy object with the necessary callback information. The Proxy
   // will take ownership of |delegate|.
   NotificationObjectProxy(
       scoped_ptr<content::DesktopNotificationDelegate> delegate);
 
   // NotificationDelegate implementation.
   void Display() override;
-  void Error() override;
   void Close(bool by_user) override;
   void Click() override;
   std::string id() const override;
 
  protected:
   ~NotificationObjectProxy() override;
 
  private:
   scoped_ptr<content::DesktopNotificationDelegate> delegate_;
   bool displayed_;
   std::string id_;
 };
 
 #endif  // CHROME_BROWSER_NOTIFICATIONS_NOTIFICATION_OBJECT_PROXY_H_