Relocate reuseable portions of ash/display/display_util.*

ash/display/unified_mouse_warp_controller_unittest.cc

Index: ash/display/unified_mouse_warp_controller_unittest.cc
diff --git a/ash/display/unified_mouse_warp_controller_unittest.cc b/ash/display/unified_mouse_warp_controller_unittest.cc
index 6b4140bf31227c52d0635651e43f5e346dbd36d0..544f8a2b6c231f80ad9dee0cca1e1775d081765c 100644
--- a/ash/display/unified_mouse_warp_controller_unittest.cc
+++ b/ash/display/unified_mouse_warp_controller_unittest.cc
@@ -15,6 +15,7 @@
 #include "ui/aura/env.h"
 #include "ui/aura/window_tree_host.h"
 #include "ui/display/display.h"
+#include "ui/display/manager/display_manager_utilities.h"
 #include "ui/display/screen.h"
 #include "ui/events/test/event_generator.h"
 #include "ui/wm/core/coordinate_conversion.h"
@@ -91,7 +92,7 @@ class UnifiedMouseWarpControllerTest : public test::AshTestBase {
     // Convert screen to the host.
     root->GetHost()->ConvertPointToHost(&new_location_in_unified_host);
 
-    int new_index = FindDisplayIndexContainingPoint(
+    int new_index = display::FindDisplayIndexContainingPoint(
         display_manager->software_mirroring_display_list(),
         new_location_in_unified_host);
     if (new_index < 0)