Add DisplayCompositorTest.

services/ui/surfaces/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("surfaces") {
   sources = [
     "direct_output_surface.cc",
     "direct_output_surface.h",
     "display_compositor.cc",
     "display_compositor.h",
     "surfaces_context_provider.cc",
     "surfaces_context_provider.h",
     "surfaces_context_provider_delegate.h",
@@ skipping 22 matching lines @@
   ]
 
   if (use_ozone) {
     sources += [
       "direct_output_surface_ozone.cc",
       "direct_output_surface_ozone.h",
     ]
     deps += [ "//gpu/command_buffer/common" ]
   }
 }
+
+test("mus_surfaces_unittests") {
+  sources = [
+    "display_compositor_unittest.cc",
+  ]
+
+  deps = [
+    ":surfaces",
+    "//base",
+    "//base/test:test_support",
+    "//cc:cc",
+    "//services/service_manager/public/cpp/test:run_all_service_tests",
+    "//testing/gtest",
+  ]
+}