ScreenWin notifies DisplayObserver's when displays changed.

ui/gfx/screen_win.h

Index: ui/gfx/screen_win.h
diff --git a/ui/gfx/screen_win.h b/ui/gfx/screen_win.h
index 7b1ea4c7bcc6021ae0f00e9a29b529cc4545ed03..951416b32bb803069a56a8c5b9efc51e13b01b98 100644
--- a/ui/gfx/screen_win.h
+++ b/ui/gfx/screen_win.h
@@ -6,6 +6,8 @@
 #define UI_GFX_SCREEN_WIN_H_
 
 #include "base/compiler_specific.h"
+#include "base/timer/timer.h"
+#include "ui/gfx/display_change_notifier.h"
 #include "ui/gfx/gfx_export.h"
 #include "ui/gfx/screen.h"
 
@@ -16,6 +18,8 @@ class GFX_EXPORT ScreenWin : public gfx::Screen {
   ScreenWin();
   virtual ~ScreenWin();
 
+  void OnDisplayChanged();
+
  protected:
   // Overridden from gfx::Screen:
   virtual bool IsDIPEnabled() OVERRIDE;
@@ -42,6 +46,22 @@ class GFX_EXPORT ScreenWin : public gfx::Screen {
   virtual NativeWindow GetNativeWindowFromHWND(HWND hwnd) const;
 
  private:
+  // Return the list of active displays.
+  std::vector<gfx::Display> BuildDisplays() const;
+
+  // Called when |configure_timer_| fires.
+  void ConfigureTimerFired();
+
+  // The timer to delay notifying DisplayObserver's when OnDisplayChanged() is
+  // called. See comment in ::OnDisplayChanged().
+  scoped_ptr<base::OneShotTimer<ScreenWin> > configure_timer_;
+
+  // Helper implementing the DisplayObserver handling.
+  gfx::DisplayChangeNotifier change_notifier_;
+
+  // Current list of displays.
+  std::vector<gfx::Display> displays_;
+
   DISALLOW_COPY_AND_ASSIGN(ScreenWin);
 };