Provide default implementations for NotificationDelegate methods.

ash/system/chromeos/screen_security/screen_tray_item.cc

Index: ash/system/chromeos/screen_security/screen_tray_item.cc
diff --git a/ash/system/chromeos/screen_security/screen_tray_item.cc b/ash/system/chromeos/screen_security/screen_tray_item.cc
index f6ac38cbe686def078e2f13d62d85bb6aa272e06..2b3667d7bd8fa9645e3d718d73fe174e55ec5b80 100644
--- a/ash/system/chromeos/screen_security/screen_tray_item.cc
+++ b/ash/system/chromeos/screen_security/screen_tray_item.cc
@@ -116,18 +116,6 @@ ScreenNotificationDelegate::ScreenNotificationDelegate(
 ScreenNotificationDelegate::~ScreenNotificationDelegate() {
 }
 
-void ScreenNotificationDelegate::Display() {
-}
-
-void ScreenNotificationDelegate::Error() {
-}
-
-void ScreenNotificationDelegate::Close(bool by_user) {
-}
-
-void ScreenNotificationDelegate::Click() {
-}
-
 void ScreenNotificationDelegate::ButtonClick(int button_index) {
   DCHECK_EQ(0, button_index);
   screen_tray_->Stop();