Replace WmWindowObserver with aura::WindowObserver.

ash/common/wm/mru_window_tracker.h

 // Copyright 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_COMMON_WM_MRU_WINDOW_TRACKER_H_
 #define ASH_COMMON_WM_MRU_WINDOW_TRACKER_H_
 
 #include <list>
 #include <vector>
 
 #include "ash/ash_export.h"
 #include "ash/common/wm_activation_observer.h"
-#include "ash/common/wm_window_observer.h"
 #include "base/macros.h"
+#include "ui/aura/window_observer.h"
 
 namespace ash {
 
 class WmWindow;
 
 // Maintains a most recently used list of windows. This is used for window
 // cycling using Alt+Tab and overview mode.
 class ASH_EXPORT MruWindowTracker : public WmActivationObserver,
-                                    public WmWindowObserver {
+                                    public aura::WindowObserver {
  public:
   using WindowList = std::vector<WmWindow*>;
 
   MruWindowTracker();
   ~MruWindowTracker() override;
 
   // Returns the set of windows which can be cycled through using the tracked
   // list of most recently used windows.
   WindowList BuildMruWindowList() const;
 
@@ skipping 10 matching lines @@
 
  private:
   // Updates the mru_windows_ list to insert/move |active_window| at/to the
   // front.
   void SetActiveWindow(WmWindow* active_window);
 
   // Overridden from WmActivationObserver:
   void OnWindowActivated(WmWindow* gained_active,
                          WmWindow* lost_active) override;
 
-  // Overridden from WmWindowObserver:
-  void OnWindowDestroyed(WmWindow* window) override;
+  // Overridden from aura::WindowObserver:
+  void OnWindowDestroyed(aura::Window* window) override;
 
   // List of windows that have been activated in containers that we cycle
   // through, sorted by most recently used.
   std::list<WmWindow*> mru_windows_;
 
   bool ignore_window_activations_;
 
   DISALLOW_COPY_AND_ASSIGN(MruWindowTracker);
 };
 
 }  // namespace ash
 
 #endif  // ASH_COMMON_WM_MRU_WINDOW_TRACKER_H_