Provide default implementations for NotificationDelegate methods.

chrome/browser/notifications/extension_welcome_notification.cc

 // Copyright 2014 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 "chrome/browser/notifications/extension_welcome_notification.h"
 
 #include "base/guid.h"
 #include "base/lazy_instance.h"
 #include "base/message_loop/message_loop.h"
 #include "base/prefs/pref_service.h"
@@ skipping 29 matching lines @@
       const message_center::NotifierId notifier_id,
       const std::string& welcome_notification_id,
       ExtensionWelcomeNotification::Delegate* delegate)
       : profile_(profile),
         notifier_id_(notifier_id.type, notifier_id.id),
         welcome_notification_id_(welcome_notification_id),
         delegate_(delegate) {
   }
 
   // Overridden from NotificationDelegate:
-  void Display() override {}
-  void Error() override {}
-
   void Close(bool by_user) override {
     if (by_user) {
       // Setting the preference here may cause the notification erasing
       // to reenter. Posting a task avoids this issue.
       delegate_->PostTask(
           FROM_HERE,
           base::Bind(&NotificationCallbacks::MarkAsDismissed, this));
     }
   }
 
-  void Click() override {}
   void ButtonClick(int index) override {
     if (index == 0) {
       OpenNotificationLearnMoreTab();
     } else if (index == 1) {
       DisableNotificationProvider();
       Close(true);
     } else {
       NOTREACHED();
     }
   }
@@ skipping 281 matching lines @@
       prefs::kWelcomeNotificationExpirationTimestamp,
       (delegate_->GetCurrentTime() +
           base::TimeDelta::FromDays(kRequestedShowTimeDays)).ToInternalValue());
 }
 
 bool ExtensionWelcomeNotification::IsWelcomeNotificationExpired() const {
   const base::Time expiration_timestamp = GetExpirationTimestamp();
   return !expiration_timestamp.is_null() &&
          (expiration_timestamp <= delegate_->GetCurrentTime());
 }