Provide default implementations for NotificationDelegate methods.

chrome/browser/status_icons/desktop_notification_balloon.cc

Index: chrome/browser/status_icons/desktop_notification_balloon.cc
diff --git a/chrome/browser/status_icons/desktop_notification_balloon.cc b/chrome/browser/status_icons/desktop_notification_balloon.cc
index 25162b349bbd18ce340d9c43a143191b1a56a8d5..1974b649683a3cd8d4523cea2a0a61a8b58b3e4a 100644
--- a/chrome/browser/status_icons/desktop_notification_balloon.cc
+++ b/chrome/browser/status_icons/desktop_notification_balloon.cc
@@ -45,9 +45,6 @@ class DummyNotificationDelegate : public NotificationDelegate {
             &CloseBalloon, id(), NotificationUIManager::GetProfileID(profile_)),
         base::TimeDelta::FromSeconds(kTimeoutSeconds));
   }
-  void Error() override {}
-  void Close(bool by_user) override {}
-  void Click() override {}
   std::string id() const override { return id_; }
 
  private: