mash: Move SystemTrayDelegate and dependencies to //ash/common

ash/common/system/update/update_observer.h

Index: ash/common/system/update/update_observer.h
diff --git a/ash/system/user/update_observer.h b/ash/common/system/update/update_observer.h
similarity index 71%
rename from ash/system/user/update_observer.h
rename to ash/common/system/update/update_observer.h
index dacf1984dd20d568563bba8d9252d60aaa5c8745..3b134e01f43ed833a6447699727aba493f672184 100644
--- a/ash/system/user/update_observer.h
+++ b/ash/common/system/update/update_observer.h
@@ -2,8 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#ifndef ASH_SYSTEM_USER_UPDATE_OBSERVER_H_
-#define ASH_SYSTEM_USER_UPDATE_OBSERVER_H_
+#ifndef ASH_COMMON_SYSTEM_UPDATE_UPDATE_OBSERVER_H_
+#define ASH_COMMON_SYSTEM_UPDATE_UPDATE_OBSERVER_H_
 
 #include "ash/ash_export.h"
 
@@ -20,4 +20,4 @@ class ASH_EXPORT UpdateObserver {
 
 }  // namespace ash
 
-#endif  //ASH_SYSTEM_USER_UPDATE_OBSERVER_H_
+#endif  //ASH_COMMON_SYSTEM_UPDATE_UPDATE_OBSERVER_H_