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

ash/common/wm_activation_observer.h

 // Copyright 2016 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_WM_ACTIVATION_OBSERVER_H_
-#define ASH_WM_ACTIVATION_OBSERVER_H_
+#ifndef ASH_COMMON_WM_ACTIVATION_OBSERVER_H_
+#define ASH_COMMON_WM_ACTIVATION_OBSERVER_H_
 
 #include "ash/ash_export.h"
 
 namespace ash {
 
 class WmWindow;
 
 // Used to track changes in activation.
 class ASH_EXPORT WmActivationObserver {
  public:
   virtual void OnWindowActivated(WmWindow* gained_active,
                                  WmWindow* lost_active) {}
 
   // Called when during window activation the currently active window is
   // selected for activation. This can happen when a window requested for
   // activation cannot be activated because a system modal window is active.
   virtual void OnAttemptToReactivateWindow(WmWindow* request_active,
                                            WmWindow* actual_active) {}
 
  protected:
   virtual ~WmActivationObserver() {}
 };
 
 }  // namespace ash
 
-#endif  // ASH_WM_ACTIVATION_OBSERVER_H_
+#endif  // ASH_COMMON_WM_ACTIVATION_OBSERVER_H_