mash: Introduce WmSystemTrayNotifier for //ash/common

ash/system/tray/system_tray_notifier.cc

Index: ash/system/tray/system_tray_notifier.cc
diff --git a/ash/system/tray/system_tray_notifier.cc b/ash/system/tray/system_tray_notifier.cc
index a902d6fd435297326e4980a4b951241eb609b95e..d81c72fe11a1b3da9c55ecb3df12cb0eacb2dfa1 100644
--- a/ash/system/tray/system_tray_notifier.cc
+++ b/ash/system/tray/system_tray_notifier.cc
@@ -62,14 +62,6 @@ void SystemTrayNotifier::RemoveTracingObserver(TracingObserver* observer) {
   tracing_observers_.RemoveObserver(observer);
 }
 
-void SystemTrayNotifier::AddUpdateObserver(UpdateObserver* observer) {
-  update_observers_.AddObserver(observer);
-}
-
-void SystemTrayNotifier::RemoveUpdateObserver(UpdateObserver* observer) {
-  update_observers_.RemoveObserver(observer);
-}
-
 void SystemTrayNotifier::AddUserObserver(UserObserver* observer) {
   user_observers_.AddObserver(observer);
 }
@@ -280,11 +272,6 @@ void SystemTrayNotifier::NotifyLocaleChanged(
       OnLocaleChanged(delegate, cur_locale, from_locale, to_locale));
 }
 
-void SystemTrayNotifier::NotifyUpdateRecommended(const UpdateInfo& info) {
-  FOR_EACH_OBSERVER(
-      UpdateObserver, update_observers_, OnUpdateRecommended(info));
-}
-
 void SystemTrayNotifier::NotifyUserUpdate() {
   FOR_EACH_OBSERVER(UserObserver,
                     user_observers_,