Remove the OnError method from notification delegates.

ui/message_center/notification_delegate.cc

Index: ui/message_center/notification_delegate.cc
diff --git a/ui/message_center/notification_delegate.cc b/ui/message_center/notification_delegate.cc
index 09ef959dbf0c173c25ac9096117b12c8fd61577c..b4b6cf7ff14c72c040859a2e3846bf264c45fad9 100644
--- a/ui/message_center/notification_delegate.cc
+++ b/ui/message_center/notification_delegate.cc
@@ -25,9 +25,6 @@ HandleNotificationClickedDelegate::~HandleNotificationClickedDelegate() {
 void HandleNotificationClickedDelegate::Display() {
 }
 
-void HandleNotificationClickedDelegate::Error() {
-}
-
 void HandleNotificationClickedDelegate::Close(bool by_user) {
 }
 
@@ -57,9 +54,6 @@ HandleNotificationButtonClickDelegate::
 void HandleNotificationButtonClickDelegate::Display() {
 }
 
-void HandleNotificationButtonClickDelegate::Error() {
-}
-
 void HandleNotificationButtonClickDelegate::Close(bool by_user) {
 }