Add ozone_unittests to the build.

ui/ozone/platform/drm/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/linux/pkg_config.gni")
 import("//ui/ozone/ozone.gni")
 
 declare_args() {
   use_mesa_platform_null = false
   use_drm_atomic = false
@@ skipping 138 matching lines @@
       ":drm_common",
       "//base",
       "//skia",
       "//ui/base",
       "//ui/ozone:ozone_base",
       "//ui/events/ozone:events_ozone",
       "//ui/events/ozone:events_ozone_evdev",
       "//ui/events/ozone:events_ozone_layout",
     ]
   }
+}
 
+if (ozone_platform_dri || ozone_platform_drm || ozone_platform_gbm) {
   source_set("drm_unittests") {
     testonly = true
     sources = [
       "gpu/drm_surface_unittest.cc",
       "gpu/drm_window_unittest.cc",
       "gpu/hardware_display_controller_unittest.cc",
       "gpu/hardware_display_plane_manager_unittest.cc",
       "gpu/screen_manager_unittest.cc",
       "test/mock_drm_device.cc",
       "test/mock_drm_device.h",
     ]
 
     deps = [
       "//base",
+      "//mojo/public/c/system:for_shared_library",
       "//skia",
       "//testing/gtest",
+      "//ui/ozone",
       "//ui/ozone:ozone_base",
       "//ui/ozone/platform/drm:drm_common",
     ]
 
     public_configs = [ ":libdrm" ]
   }
 }
 
 if (ozone_platform_gbm) {
   pkg_config("libgbm") {
@@ skipping 33 matching lines @@
     public_configs = [
       ":libgbm",
       "//third_party/khronos:khronos_headers",
     ]
 
     if (use_mesa_platform_null) {
       defines += [ "USE_MESA_PLATFORM_NULL" ]
     }
   }
 }