Relocate display_manager from ash to ui

Move display_manager from ash to ui so that it can be used in mus and in
ash.

BUG=581462

Review-Url: https://codereview.chromium.org/2445583002
Cr-Commit-Position: refs/heads/master@{#428567}
diff --git a/ash/magnifier/partial_magnification_controller_unittest.cc b/ash/magnifier/partial_magnification_controller_unittest.cc
index 7e6e3aa..72ce87a4 100644
--- a/ash/magnifier/partial_magnification_controller_unittest.cc
+++ b/ash/magnifier/partial_magnification_controller_unittest.cc
@@ -2,11 +2,11 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#include "ash/display/display_manager.h"
 #include "ash/magnifier/magnification_controller.h"
 #include "ash/magnifier/partial_magnification_controller.h"
 #include "ash/shell.h"
 #include "ash/test/ash_test_base.h"
+#include "ui/display/manager/display_manager.h"
 #include "ui/events/test/event_generator.h"
 #include "ui/views/widget/widget.h"