Converts ShellObserver from aura::Window to ash::WmWindow

ash/wm/screen_dimmer.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_WM_SCREEN_DIMMER_H_
 #define ASH_WM_SCREEN_DIMMER_H_
 
 #include "ash/ash_export.h"
 #include "ash/shell_observer.h"
 #include "base/compiler_specific.h"
@@ skipping 35 matching lines @@
 
   // Find a ScreenDimmer in the container, or nullptr if it does not exist.
   static ScreenDimmer* FindForTest(int container_id);
 
  private:
   static aura::Window* FindContainer(int container_id);
 
   explicit ScreenDimmer(int container_id);
 
   // ShellObserver:
-  void OnRootWindowAdded(aura::Window* root_window) override;
+  void OnRootWindowAdded(WmWindow* root_window) override;
 
   // Update the dimming state. This will also create a new DimWindow
   // if necessary. (Used when a new display is connected)
   void Update(bool should_dim);
 
   int container_id_;
   float target_opacity_;
 
   // Are we currently dimming the screen?
   bool is_dimming_;
   bool at_bottom_;
 
   DISALLOW_COPY_AND_ASSIGN(ScreenDimmer);
 };
 
 }  // namespace ash
 
 #endif  // ASH_WM_SCREEN_DIMMER_H_