Find display root ServerWindow for located events in mus.

ash/mus/root_window_controller.cc

Index: ash/mus/root_window_controller.cc
diff --git a/ash/mus/root_window_controller.cc b/ash/mus/root_window_controller.cc
index 42b0f049b913f37c5dba993da7a17064e1b8826c..f8d6340502933025eda54c5cfb2e935332d247a9 100644
--- a/ash/mus/root_window_controller.cc
+++ b/ash/mus/root_window_controller.cc
@@ -224,7 +224,9 @@ void RootWindowController::CreateStatusArea() {
   status_area_widget->CreateTrayViews();
   // TODO(jamescook): Remove this when ash::StatusAreaLayoutManager and
   // ash::ShelfLayoutManager are working in mash. http://crbug.com/621112
-  status_area_widget->SetBounds(gfx::Rect(845, 720, 120, 40));
+  gfx::Size display_size = display_.bounds().size();
+  status_area_widget->SetBounds(gfx::Rect(display_size.width() - 179,
+                                          display_size.height() - 48, 120, 40));
   if (WmShell::Get()->GetSessionStateDelegate()->IsActiveUserSessionStarted())
     status_area_widget->Show();
 }