Revert "chromeos: Move files in //ash/common to //ash, part 3"

ash/session/session_state_observer.h

-// Copyright (c) 2013 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_SESSION_SESSION_STATE_OBSERVER_H_
-#define ASH_SESSION_SESSION_STATE_OBSERVER_H_
-
-#include "ash/ash_export.h"
-#include "base/macros.h"
-#include "components/session_manager/session_manager_types.h"
-
-class AccountId;
-
-namespace ash {
-
-class ASH_EXPORT SessionStateObserver {
- public:
-  // Called when active user has changed.
-  virtual void ActiveUserChanged(const AccountId& account_id) {}
-
-  // Called when another user gets added to the existing session.
-  virtual void UserAddedToSession(const AccountId& account_id) {}
-
-  // Called when session state is changed.
-  virtual void SessionStateChanged(session_manager::SessionState state) {}
-
- protected:
-  virtual ~SessionStateObserver() {}
-};
-
-// A class to attach / detach an object as a session state observer.
-class ASH_EXPORT ScopedSessionStateObserver {
- public:
-  explicit ScopedSessionStateObserver(SessionStateObserver* observer);
-  virtual ~ScopedSessionStateObserver();
-
- private:
-  ash::SessionStateObserver* observer_;
-
-  DISALLOW_COPY_AND_ASSIGN(ScopedSessionStateObserver);
-};
-
-}  // namespace ash
-
-#endif  // ASH_SESSION_SESSION_STATE_OBSERVER_H_