Move DisplayManager and DisplayChangeObserverX11 from aura to ash.

ui/aura/root_window.cc

Index: ui/aura/root_window.cc
diff --git a/ui/aura/root_window.cc b/ui/aura/root_window.cc
index 6c08fe6593387b6e5da2d788ce20a966cd3e1d2c..c646df054db89f3de1cc1e25ea8d218ba75d4922 100644
--- a/ui/aura/root_window.cc
+++ b/ui/aura/root_window.cc
@@ -18,7 +18,6 @@
 #include "ui/aura/client/cursor_client.h"
 #include "ui/aura/client/event_client.h"
 #include "ui/aura/client/screen_position_client.h"
-#include "ui/aura/display_manager.h"
 #include "ui/aura/env.h"
 #include "ui/aura/event_filter.h"
 #include "ui/aura/focus_manager.h"
@@ -69,9 +68,9 @@ void GetEventFiltersToNotify(Window* target, EventFilters* filters) {
   }
 }
 
-float GetDeviceScaleFactorFromDisplay(const Window* window) {
-  DisplayManager* display_manager = Env::GetInstance()->display_manager();
-  return display_manager->GetDisplayNearestWindow(window).device_scale_factor();
+float GetDeviceScaleFactorFromDisplay(Window* window) {
+  return gfx::Screen::GetScreenFor(window)->
+      GetDisplayNearestWindow(window).device_scale_factor();
 }
 
 Window* ConsumerToWindow(ui::GestureConsumer* consumer) {