Adding NOTREACHED to see if any of the methods are called

ui/message_center/notification_delegate.cc

 // 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.
 
 #include "ui/message_center/notification_delegate.h"
 
 #include "base/logging.h"
 
 namespace message_center {
 
 // NotificationDelegate:
 
-void NotificationDelegate::Display() {}
+void NotificationDelegate::Display() {
+  NOTREACHED();
+}
 
-void NotificationDelegate::Close(bool by_user) {}
+void NotificationDelegate::Close(bool by_user) {
+  NOTREACHED();
+}
 
-bool NotificationDelegate::HasClickedListener() { return false; }
+bool NotificationDelegate::HasClickedListener() {
+  NOTREACHED();
+  return false;
+}
 
-void NotificationDelegate::Click() {}
+void NotificationDelegate::Click() {
+  NOTREACHED();
+}
 
-void NotificationDelegate::ButtonClick(int button_index) {}
+void NotificationDelegate::ButtonClick(int button_index) {
+  NOTREACHED();
+}
 
 void NotificationDelegate::ButtonClickWithReply(int button_index,
                                                 const base::string16& reply) {
   NOTIMPLEMENTED();
 }
 
 void NotificationDelegate::SettingsClick() {}
 
 bool NotificationDelegate::ShouldDisplaySettingsButton() {
   return false;
@@ skipping 30 matching lines @@
 void HandleNotificationButtonClickDelegate::ButtonClick(int button_index) {
   if (!button_callback_.is_null())
     button_callback_.Run(button_index);
 }
 
 bool NotificationDelegate::ShouldDisplayOverFullscreen() const {
   return false;
 }
 
 }  // namespace message_center