ash: Fix system tray avatar not updated regression

ash/common/system/user/user_observer.h

Index: ash/common/system/user/user_observer.h
diff --git a/ash/common/system/user/user_observer.h b/ash/common/system/user/user_observer.h
deleted file mode 100644
index 8c30606fa010e545e7a0dea6fbe77e2bea7b0042..0000000000000000000000000000000000000000
--- a/ash/common/system/user/user_observer.h
+++ /dev/null
@@ -1,25 +0,0 @@
-// Copyright (c) 2012 The Chromium Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-#ifndef ASH_COMMON_SYSTEM_USER_USER_OBSERVER_H_
-#define ASH_COMMON_SYSTEM_USER_USER_OBSERVER_H_
-
-#include "ash/ash_export.h"
-
-namespace ash {
-
-class ASH_EXPORT UserObserver {
- public:
-  virtual ~UserObserver() {}
-
-  // A user got updated / changed.
-  virtual void OnUserUpdate() = 0;
-
-  // A user was added to the existing session.
-  virtual void OnUserAddedToSession() = 0;
-};
-
-}  // namespace ash
-
-#endif  // ASH_COMMON_SYSTEM_USER_USER_OBSERVER_H_