Revert of 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 5f3af6ba1ae63d9e4b5380956ad9427174980b6a..e530b8c43a4c3e484b8b9b2ca9d39beb8fd64639 100644
--- a/ash/common/system/tray/system_tray_notifier.cc
+++ b/ash/common/system/tray/system_tray_notifier.cc
@@ -7,6 +7,7 @@
 #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)
@@ -92,6 +93,19 @@
     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);
 }