Refactors DimWindow and moves to ash/common

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 <memory>
+
 #include "ash/ash_export.h"
 #include "ash/common/shell_observer.h"
 #include "base/compiler_specific.h"
 #include "base/macros.h"
 #include "ui/aura/window_observer.h"
 
 namespace ui {
 class Layer;
 }
 
 namespace ash {
-class DimWindow;
+namespace test {
+class ScreenDimmerTest;
+}
+
+class WindowDimmer;
+
+template <typename UserData>
+class WmWindowUserData;
 
 // ScreenDimmer displays a partially-opaque layer above everything
 // else in the given container window to darken the display.  It shouldn't be
 // used for long-term brightness adjustments due to performance
 // considerations -- it's only intended for cases where we want to
 // briefly dim the screen (e.g. to indicate to the user that we're
 // about to suspend a machine that lacks an internal backlight that
 // can be adjusted).
-class ASH_EXPORT ScreenDimmer : ShellObserver {
+class ASH_EXPORT ScreenDimmer : public ShellObserver {
  public:
   // Creates a screen dimmer for the containers given by |container_id|.
   // It's owned by the container in the primary root window and will be
   // destroyed when the container is destroyed.
   static ScreenDimmer* GetForContainer(int container_id);
 
   // Creates a dimmer a root window level. This is used for suspend animation.
   static ScreenDimmer* GetForRoot();
 
   ~ScreenDimmer() override;
 
   // Dim or undim the layers.
   void SetDimming(bool should_dim);
 
   void set_at_bottom(bool at_bottom) { at_bottom_ = at_bottom; }
 
   bool is_dimming() const { return is_dimming_; }
 
   // 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);
+  friend class test::ScreenDimmerTest;
 
   explicit ScreenDimmer(int container_id);
 
+  static aura::Window* FindContainer(int container_id);
+
   // ShellObserver:
   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_;
 
+  // Owns the WindowDimmers.
+  std::unique_ptr<WmWindowUserData<WindowDimmer>> window_dimmers_;
+
   DISALLOW_COPY_AND_ASSIGN(ScreenDimmer);
 };
 
 }  // namespace ash
 
 #endif  // ASH_WM_SCREEN_DIMMER_H_