Provide default implementations for NotificationDelegate methods.

ash/display/resolution_notification_controller.cc

Index: ash/display/resolution_notification_controller.cc
diff --git a/ash/display/resolution_notification_controller.cc b/ash/display/resolution_notification_controller.cc
index 35ee07b569e5dd5dddc823dc7dd8a44e1eabe2d4..82de8e0346c6ee78e1cd6b0f5674ef0e15d70c07 100644
--- a/ash/display/resolution_notification_controller.cc
+++ b/ash/display/resolution_notification_controller.cc
@@ -40,8 +40,6 @@ class ResolutionChangeNotificationDelegate
 
  private:
   // message_center::NotificationDelegate overrides:
-  virtual void Display() override;
-  virtual void Error() override;
   virtual void Close(bool by_user) override;
   virtual void Click() override;
   virtual bool HasClickedListener() override;
@@ -64,12 +62,6 @@ ResolutionChangeNotificationDelegate::ResolutionChangeNotificationDelegate(
 ResolutionChangeNotificationDelegate::~ResolutionChangeNotificationDelegate() {
 }
 
-void ResolutionChangeNotificationDelegate::Display() {
-}
-
-void ResolutionChangeNotificationDelegate::Error() {
-}
-
 void ResolutionChangeNotificationDelegate::Close(bool by_user) {
   if (by_user)
     controller_->AcceptResolutionChange(false);