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

ash/common/system/date/clock_observer.h

 // 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_SYSTEM_DATE_CLOCK_OBSERVER_H_
-#define ASH_SYSTEM_DATE_CLOCK_OBSERVER_H_
+#ifndef ASH_COMMON_SYSTEM_DATE_CLOCK_OBSERVER_H_
+#define ASH_COMMON_SYSTEM_DATE_CLOCK_OBSERVER_H_
 
 #include "ash/ash_export.h"
 
 namespace ash {
 
 class ASH_EXPORT ClockObserver {
  public:
   virtual ~ClockObserver() {}
 
   virtual void OnDateFormatChanged() = 0;
   virtual void OnSystemClockTimeUpdated() = 0;
   virtual void OnSystemClockCanSetTimeChanged(bool can_set_time) = 0;
 
   // Force a refresh (e.g. after the system is resumed).
   virtual void Refresh() = 0;
 };
 
 }  // namespace ash
 
-#endif  // ASH_SYSTEM_DATE_CLOCK_OBSERVER_H_
+#endif  // ASH_COMMON_SYSTEM_DATE_CLOCK_OBSERVER_H_