Verify that the notification response contains sensible data

chrome/browser/notifications/notification_operation_common.h

 // Copyright 2016 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_OPERATION_COMMON_H_
 #define CHROME_BROWSER_NOTIFICATIONS_NOTIFICATION_OPERATION_COMMON_H_
 
 // A series of common operations for both in page and persistent notification
 namespace content {
 class BrowserContext;
 }  // namespace content
 
 namespace notification_operation_common {
 
 // Things you can do to a notification.
 enum NotificationOperation {
   NOTIFICATION_CLICK = 0,
   NOTIFICATION_CLOSE = 1,
-  NOTIFICATION_SETTINGS = 2
+  NOTIFICATION_SETTINGS = 2,
+  NOTIFICATION_OPERATION_MAX = NOTIFICATION_SETTINGS
 };
 
 // Open the Notification settings screen when clicking the right button.
 void OpenNotificationSettings(content::BrowserContext* browser_context);
 
 }  // namespace notification_operation_common
 
 #endif  // CHROME_BROWSER_NOTIFICATIONS_NOTIFICATION_OPERATION_COMMON_H_