Replace WmWindowObserver with aura::WindowObserver.

ash/common/wm/window_dimmer.h

 // Copyright 2015 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_WINDOW_DIMMER_H_
 #define ASH_COMMON_WINDOW_DIMMER_H_
 
 #include "ash/ash_export.h"
-#include "ash/common/wm_window_observer.h"
 #include "base/macros.h"
+#include "ui/aura/window_observer.h"
 
 namespace ash {
 
+class WmWindow;
+
 // WindowDimmer creates a window whose opacity is animated by way of
 // SetDimOpacity() and whose size matches that of its parent. WindowDimmer is
 // intended to be used in cases where a certain set of windows need to appear
 // partially obscured. This is achieved by creating WindowDimmer, setting the
 // opacity, and then stacking window() above the windows that are to appear
 // obscured. The window created by WindowDimmer is owned by the parent, but also
 // deleted if WindowDimmer is deleted. It is expected that WindowDimmer is
 // deleted when the parent window is deleted (such as happens with
 // WmWindowUserData).
-class ASH_EXPORT WindowDimmer : public WmWindowObserver {
+class ASH_EXPORT WindowDimmer : public aura::WindowObserver {
  public:
   // Creates a new WindowDimmer. The window() created by WindowDimmer is added
   // to |parent| and stacked above all other child windows.
   explicit WindowDimmer(WmWindow* parent);
   ~WindowDimmer() override;
 
   void SetDimOpacity(float target_opacity);
 
   WmWindow* parent() { return parent_; }
   WmWindow* window() { return window_; }
 
   // NOTE: WindowDimmer is an observer for both |parent_| and |window_|.
-  // WmWindowObserver:
-  void OnWindowBoundsChanged(WmWindow* window,
+  // aura::WindowObserver:
+  void OnWindowBoundsChanged(aura::Window* window,
                              const gfx::Rect& old_bounds,
                              const gfx::Rect& new_bounds) override;
-  void OnWindowDestroying(WmWindow* window) override;
-  void OnWindowTreeChanging(WmWindow* window,
-                            const TreeChangeParams& params) override;
+  void OnWindowDestroying(aura::Window* window) override;
+  void OnWindowHierarchyChanging(const HierarchyChangeParams& params) override;
 
  private:
   WmWindow* parent_;
   WmWindow* window_;
 
   DISALLOW_COPY_AND_ASSIGN(WindowDimmer);
 };
 
 }  // namespace ash
 
 #endif  // ASH_COMMON_WINDOW_DIMMER_H_