Remove dead code related to Notification View Bubble

ash/common/system/tray/system_tray.cc

Index: ash/common/system/tray/system_tray.cc
diff --git a/ash/common/system/tray/system_tray.cc b/ash/common/system/tray/system_tray.cc
index 9ece5f052771edcbc441f57b51724f536d53659f..3dc94551a675925c5927e400dd7eebd03e53f20b 100644
--- a/ash/common/system/tray/system_tray.cc
+++ b/ash/common/system/tray/system_tray.cc
@@ -494,13 +494,6 @@ TrayAudio* SystemTray::GetTrayAudio() const {
   return tray_audio_;
 }
 
-bool SystemTray::CloseNotificationBubbleForTest() const {
-  if (!notification_bubble_)
-    return false;
-  notification_bubble_->bubble()->Close();
-  return true;
-}
-
 // Private methods.
 
 bool SystemTray::HasSystemBubbleType(SystemTrayBubble::BubbleType type) {