Remove the OnError method from notification delegates.

ui/message_center/notification_delegate.h

Index: ui/message_center/notification_delegate.h
diff --git a/ui/message_center/notification_delegate.h b/ui/message_center/notification_delegate.h
index f870fcb4d18f1f14b671ae3c066cadd7259f2f13..0d902b22d7e0802634840b070244582145085c75 100644
--- a/ui/message_center/notification_delegate.h
+++ b/ui/message_center/notification_delegate.h
@@ -26,10 +26,6 @@ class MESSAGE_CENTER_EXPORT NotificationDelegate
   // To be called when the desktop notification is actually shown.
   virtual void Display() = 0;
 
-  // To be called when the desktop notification cannot be shown due to an
-  // error.
-  virtual void Error() = 0;
-
   // 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) = 0;
@@ -60,7 +56,6 @@ class MESSAGE_CENTER_EXPORT HandleNotificationClickedDelegate
 
   // message_center::NotificationDelegate overrides:
   void Display() override;
-  void Error() override;
   void Close(bool by_user) override;
   bool HasClickedListener() override;
   void Click() override;
@@ -88,7 +83,6 @@ class MESSAGE_CENTER_EXPORT HandleNotificationButtonClickDelegate
 
   // message_center::NotificationDelegate overrides:
   void Display() override;
-  void Error() override;
   void Close(bool by_user) override;
   void Click() override;
   void ButtonClick(int button_index) override;