Reland: ash: Use system tray mojo interface to show system update tray icon

ash/common/system/tray/system_tray_notifier.cc

Index: ash/common/system/tray/system_tray_notifier.cc
diff --git a/ash/common/system/tray/system_tray_notifier.cc b/ash/common/system/tray/system_tray_notifier.cc
index 665beda7355c4d81eb9b997f41de588d08073c91..c443605ff14af649212d375c863ee10dc7f58c1e 100644
--- a/ash/common/system/tray/system_tray_notifier.cc
+++ b/ash/common/system/tray/system_tray_notifier.cc
@@ -7,7 +7,6 @@
 #include "ash/common/system/accessibility_observer.h"
 #include "ash/common/system/date/clock_observer.h"
 #include "ash/common/system/ime/ime_observer.h"
-#include "ash/common/system/update/update_observer.h"
 #include "ash/common/system/user/user_observer.h"
 
 #if defined(OS_CHROMEOS)
@@ -92,19 +91,6 @@ void SystemTrayNotifier::NotifyRefreshIMEMenu(bool is_active) {
     observer.OnIMEMenuActivationChanged(is_active);
 }
 
-void SystemTrayNotifier::AddUpdateObserver(UpdateObserver* observer) {
-  update_observers_.AddObserver(observer);
-}
-
-void SystemTrayNotifier::RemoveUpdateObserver(UpdateObserver* observer) {
-  update_observers_.RemoveObserver(observer);
-}
-
-void SystemTrayNotifier::NotifyUpdateRecommended(const UpdateInfo& info) {
-  for (auto& observer : update_observers_)
-    observer.OnUpdateRecommended(info);
-}
-
 void SystemTrayNotifier::AddUserObserver(UserObserver* observer) {
   user_observers_.AddObserver(observer);
 }