Changes how window manager obtains WindowTree from mus

components/mus/public/cpp/tests/BUILD.gn

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//build/config/ui.gni")
 import("//testing/test.gni")
 
 source_set("unittest_support") {
   testonly = true
 
   sources = [
     "test_window.h",
     "test_window_tree.cc",
     "test_window_tree.h",
     "test_window_tree_client_setup.cc",
     "test_window_tree_client_setup.h",
     "window_tree_client_private.cc",
     "window_tree_client_private.h",
   ]
 
   deps = [
     "//base",
     "//components/mus/public/cpp",
     "//testing/gtest",
+    "//ui/display",
     "//ui/gfx/geometry/mojo",
   ]
 }
 
 source_set("test_support") {
   testonly = true
 
   sources = [
     "window_server_shelltest_base.cc",
     "window_server_shelltest_base.h",
@@ skipping 37 matching lines @@
     "//ui/events",
     "//ui/gfx:test_support",
     "//ui/gfx/geometry",
     "//ui/gfx/geometry/mojo",
   ]
 
   if (use_x11) {
     deps += [ "//ui/gfx/x" ]
   }
 }