mash: Migrate some system user files to common.

ash/system/tray/system_tray.h

Index: ash/system/tray/system_tray.h
diff --git a/ash/system/tray/system_tray.h b/ash/system/tray/system_tray.h
index e733fb61a05af1371b8b28220f6c2d7b95977fde..1cee188783d8a0a77ee7d3c7c0abc828f576bc0e 100644
--- a/ash/system/tray/system_tray.h
+++ b/ash/system/tray/system_tray.h
@@ -13,13 +13,14 @@
 #include "ash/common/system/tray/system_tray_bubble.h"
 #include "ash/common/system/tray/tray_background_view.h"
 #include "ash/system/cast/tray_cast.h"
-#include "ash/system/user/login_status.h"
 #include "base/macros.h"
 #include "base/memory/scoped_vector.h"
 #include "ui/views/bubble/tray_bubble_view.h"
 #include "ui/views/view.h"
 
 namespace ash {
+
+enum class LoginStatus;
 class ScreenTrayItem;
 class StatusAreaWidget;
 class SystemBubbleWrapper;