Revert "chromeos: Move files in //ash/common to //ash, part 1"

ash/system/session/session_length_limit_observer.h

Index: ash/system/session/session_length_limit_observer.h
diff --git a/ash/system/session/session_length_limit_observer.h b/ash/system/session/session_length_limit_observer.h
deleted file mode 100644
index 610feb41002eb1504efce6fa983b7b4c880c648a..0000000000000000000000000000000000000000
--- a/ash/system/session/session_length_limit_observer.h
+++ /dev/null
@@ -1,26 +0,0 @@
-// Copyright 2014 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_SYSTEM_SESSION_SESSION_LENGTH_LIMIT_OBSERVER_H_
-#define ASH_SYSTEM_SESSION_SESSION_LENGTH_LIMIT_OBSERVER_H_
-
-#include "ash/ash_export.h"
-
-namespace ash {
-
-// Observer for the session length limit.
-class ASH_EXPORT SessionLengthLimitObserver {
- public:
-  virtual ~SessionLengthLimitObserver() {}
-
-  // Called when the session start time is updated.
-  virtual void OnSessionStartTimeChanged() = 0;
-
-  // Called when the session length limit is updated.
-  virtual void OnSessionLengthLimitChanged() = 0;
-};
-
-}  // namespace ash
-
-#endif  // ASH_SYSTEM_SESSION_SESSION_LENGTH_LIMIT_OBSERVER_H_