Creates mus test helper class

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_connection_setup.cc",
+    "test_window_tree_connection_setup.h",
+    "window_tree_client_impl_private.cc",
+    "window_tree_client_impl_private.h",
   ]
 
   deps = [
     "//base",
     "//components/mus/public/cpp",
+    "//mojo/converters/geometry",
+    "//testing/gtest",
   ]
 }
 
 source_set("test_support") {
   testonly = true
 
   sources = [
     "window_server_shelltest_base.cc",
     "window_server_shelltest_base.h",
     "window_server_test_base.cc",
     "window_server_test_base.h",
   ]
 
   deps = [
     "//base",
     "//base/test:test_config",
     "//components/mus/common:mus_common",
     "//components/mus/public/cpp",
     "//services/shell/public/cpp:shell_test_support",
     "//services/shell/public/cpp:sources",
     "//testing/gtest",
     "//ui/gl",
   ]
 }
 
 test("mus_public_unittests") {
   sources = [
     "property_type_converters_unittest.cc",
     "run_all_unittests.cc",
-    "test_window_tree.cc",
-    "test_window_tree.h",
     "window_server_test_suite.cc",
     "window_server_test_suite.h",
     "window_tree_client_impl_unittest.cc",
     "window_unittest.cc",
   ]
 
   deps = [
     ":unittest_support",
     "//base",
     "//base/test:test_support",
@@ skipping 11 matching lines @@
     "//ui/events",
     "//ui/gfx:test_support",
     "//ui/gfx/geometry",
     "//ui/mojo/geometry:interfaces",
   ]
 
   if (use_x11) {
     deps += [ "//ui/gfx/x" ]
   }
 }