ScreenWin notifies DisplayObserver's when displays changed.

ui/views/widget/desktop_aura/desktop_window_tree_host_win.cc

Index: ui/views/widget/desktop_aura/desktop_window_tree_host_win.cc
diff --git a/ui/views/widget/desktop_aura/desktop_window_tree_host_win.cc b/ui/views/widget/desktop_aura/desktop_window_tree_host_win.cc
index acbef2b60820a32f2e22a45f852d0d75eb59f666..bf177ef31aa91cf3ce9ac21d13d2fbc0dc96bf36 100644
--- a/ui/views/widget/desktop_aura/desktop_window_tree_host_win.cc
+++ b/ui/views/widget/desktop_aura/desktop_window_tree_host_win.cc
@@ -20,6 +20,8 @@
 #include "ui/gfx/native_widget_types.h"
 #include "ui/gfx/path.h"
 #include "ui/gfx/path_win.h"
+#include "ui/gfx/screen.h"
+#include "ui/gfx/screen_win.h"
 #include "ui/gfx/vector2d.h"
 #include "ui/gfx/win/dpi.h"
 #include "ui/native_theme/native_theme_aura.h"
@@ -728,6 +730,8 @@ bool DesktopWindowTreeHostWin::HandleInitialFocus(
 
 void DesktopWindowTreeHostWin::HandleDisplayChange() {
   GetWidget()->widget_delegate()->OnDisplayChanged();
+  static_cast<gfx::ScreenWin*>(gfx::Screen::GetScreenFor(content_window_))

[sky, 2014/07/21 17:09:18]

There may be multiple DesktopWindowTreeHostWin's on this display. I also don't
think DesktopWindowTreeHostWin should be the one responsible for communicating
this state. Can you use SingletonHwnd?

[mlamouri (slow - plz ping), 2014/07/21 17:15:09]

I am using a coalescing timer in ScreenWin because of that.
I agree.
I wasn't aware of that. I will have a a look.

+      ->OnDisplayChanged();
 }
 
 void DesktopWindowTreeHostWin::HandleBeginWMSizeMove() {