ScreenWin notifies DisplayObserver's when displays changed.

ui/views/widget/desktop_aura/desktop_window_tree_host_win.cc

 // 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.
 
 #include "ui/views/widget/desktop_aura/desktop_window_tree_host_win.h"
 
 #include "base/win/metro.h"
 #include "third_party/skia/include/core/SkPath.h"
 #include "third_party/skia/include/core/SkRegion.h"
 #include "ui/aura/client/aura_constants.h"
 #include "ui/aura/client/cursor_client.h"
 #include "ui/aura/client/focus_client.h"
 #include "ui/aura/window_event_dispatcher.h"
 #include "ui/aura/window_property.h"
 #include "ui/base/cursor/cursor_loader_win.h"
 #include "ui/base/ime/input_method.h"
 #include "ui/base/win/shell.h"
 #include "ui/compositor/compositor_constants.h"
 #include "ui/gfx/insets.h"
 #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"
 #include "ui/native_theme/native_theme_win.h"
 #include "ui/views/corewm/tooltip_win.h"
 #include "ui/views/ime/input_method_bridge.h"
 #include "ui/views/widget/desktop_aura/desktop_cursor_loader_updater.h"
 #include "ui/views/widget/desktop_aura/desktop_drag_drop_client_win.h"
 #include "ui/views/widget/desktop_aura/desktop_native_cursor_manager.h"
 #include "ui/views/widget/desktop_aura/desktop_native_widget_aura.h"
@@ skipping 688 matching lines @@
   desktop_native_widget_aura_->OnHostClosed();
 }
 
 bool DesktopWindowTreeHostWin::HandleInitialFocus(
     ui::WindowShowState show_state) {
   return GetWidget()->SetInitialFocus(show_state);
 }
 
 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() {
   native_widget_delegate_->OnNativeWidgetBeginUserBoundsChange();
 }
 
 void DesktopWindowTreeHostWin::HandleEndWMSizeMove() {
   native_widget_delegate_->OnNativeWidgetEndUserBoundsChange();
 }
 
@@ skipping 205 matching lines @@
 
 // static
 DesktopWindowTreeHost* DesktopWindowTreeHost::Create(
     internal::NativeWidgetDelegate* native_widget_delegate,
     DesktopNativeWidgetAura* desktop_native_widget_aura) {
   return new DesktopWindowTreeHostWin(native_widget_delegate,
                                       desktop_native_widget_aura);
 }
 
 }  // namespace views