Moves ash/wm/common back into ash

ash/wm/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_COMMON_WM_ACTIVATION_OBSERVER_H_
 #define ASH_WM_COMMON_WM_ACTIVATION_OBSERVER_H_
 
-#include "ash/wm/common/ash_wm_common_export.h"
+#include "ash/ash_export.h"
 
 namespace ash {
 namespace wm {
 
 class WmWindow;
 
 // Used to track changes in activation.
-class ASH_WM_COMMON_EXPORT WmActivationObserver {
+class ASH_EXPORT WmActivationObserver {
  public:
   virtual void OnWindowActivated(WmWindow* gained_active,
                                  WmWindow* lost_active) = 0;
 
  protected:
   virtual ~WmActivationObserver() {}
 };
 
 }  // namespace wm
 }  // namespace ash
 
 #endif  // ASH_WM_COMMON_WM_ACTIVATION_OBSERVER_H_