Notifications: Close locale changed notification on click.

Currently, clicking on this notification marks the locale change as accepted,
but does not dismiss the notification. When the user interacts with the
notification again, it does not work.

TEST=manual
BUG=937185

Change-Id: Ib510f78d6695bf2916678673a74198df605e5900
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1693682Reviewed-by: Tetsui Ohkubo <tetsui@chromium.org>
Commit-Queue: Tim Song <tengs@chromium.org>
Cr-Commit-Position: refs/heads/master@{#676167}

ash/system/locale/locale_update_controller_impl.cc

@@ -75,6 +75,9 @@ void LocaleNotificationDelegate::Click(
 
   std::move(callback_).Run(button_index ? LocaleNotificationResult::kRevert
                                         : LocaleNotificationResult::kAccept);
+
+  message_center::MessageCenter::Get()->RemoveNotification(
+      kLocaleChangeNotificationId, true /* by_user */);
 }
 
 }  // namespace