ScreenWin notifies DisplayObserver's when displays changed.

ui/gfx/screen_win.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 UI_GFX_SCREEN_WIN_H_
 #define UI_GFX_SCREEN_WIN_H_
 
 #include "base/compiler_specific.h"
+#include "ui/gfx/display_change_notifier.h"
 #include "ui/gfx/gfx_export.h"
 #include "ui/gfx/screen.h"
+#include "ui/gfx/win/singleton_hwnd.h"
 
 namespace gfx {
 
-class GFX_EXPORT ScreenWin : public gfx::Screen {
+class GFX_EXPORT ScreenWin : public Screen,
+                             public SingletonHwnd::Observer {
  public:
   ScreenWin();
   virtual ~ScreenWin();
 
  protected:
   // Overridden from gfx::Screen:
   virtual bool IsDIPEnabled() OVERRIDE;
   virtual gfx::Point GetCursorScreenPoint() OVERRIDE;
   virtual gfx::NativeWindow GetWindowUnderCursor() OVERRIDE;
   virtual gfx::NativeWindow GetWindowAtScreenPoint(const gfx::Point& point)
       OVERRIDE;
   virtual int GetNumDisplays() const OVERRIDE;
   virtual std::vector<gfx::Display> GetAllDisplays() const OVERRIDE;
   virtual gfx::Display GetDisplayNearestWindow(
       gfx::NativeView window) const OVERRIDE;
   virtual gfx::Display GetDisplayNearestPoint(
       const gfx::Point& point) const OVERRIDE;
   virtual gfx::Display GetDisplayMatching(
       const gfx::Rect& match_rect) const OVERRIDE;
   virtual gfx::Display GetPrimaryDisplay() const OVERRIDE;
   virtual void AddObserver(DisplayObserver* observer) OVERRIDE;
   virtual void RemoveObserver(DisplayObserver* observer) OVERRIDE;
 
+  // Overriden from gfx::SingletonHwnd::Observer.
+  virtual void OnWndProc(HWND hwnd,
+                         UINT message,
+                         WPARAM wparam,
+                         LPARAM lparam) OVERRIDE;
+
   // Returns the HWND associated with the NativeView.
   virtual HWND GetHWNDFromNativeView(NativeView window) const;
 
   // Returns the NativeView associated with the HWND.
   virtual NativeWindow GetNativeWindowFromHWND(HWND hwnd) const;
 
  private:
+  // Helper implementing the DisplayObserver handling.
+  gfx::DisplayChangeNotifier change_notifier_;
+
+  // Current list of displays.
+  std::vector<gfx::Display> displays_;
+
   DISALLOW_COPY_AND_ASSIGN(ScreenWin);
 };
 
 }  // namespace gfx
 
 #endif  // UI_GFX_SCREEN_WIN_H_