Unified Desktop: hook up ash to allow unified desktop mode

ash/display/screen_ash.cc

Index: ash/display/screen_ash.cc
diff --git a/ash/display/screen_ash.cc b/ash/display/screen_ash.cc
index 700abe6e03a6b99f3af7637eb82c644ae7f052f7..5941bccfa742c156116299089cddc4d1d0232717 100644
--- a/ash/display/screen_ash.cc
+++ b/ash/display/screen_ash.cc
@@ -165,8 +165,9 @@ gfx::Display ScreenAsh::GetDisplayNearestWindow(gfx::NativeView window) const {
   DisplayManager* display_manager = GetDisplayManager();
   // RootWindow needs Display to determine its device scale factor
   // for non desktop display.
-  if (display_manager->software_mirroring_display().id() == id)
-    return display_manager->software_mirroring_display();
+  gfx::Display mirroring_display = display_manager->GetMirroringDisplayById(id);
+  if (mirroring_display.is_valid())
+    return mirroring_display;
   return display_manager->GetDisplayForId(id);
 }