[Ozone-DRI] Add display observer

ui/ozone/platform/dri/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")
 
 pkg_config("libdrm") {
   packages = [ "libdrm" ]
 }
 
 source_set("dri_common") {
   sources = [
     "channel_observer.h",
     "crtc_controller.cc",
     "crtc_controller.h",
+    "display_change_observer.h",
     "display_manager.cc",
     "display_manager.h",
     "display_mode_dri.cc",
     "display_mode_dri.h",
     "display_snapshot_dri.cc",
     "display_snapshot_dri.h",
     "dri_console_buffer.cc",
     "dri_console_buffer.h",
     "dri_cursor.cc",
     "dri_cursor.h",
@@ skipping 120 matching lines @@
       ":dri_common",
       "//base",
       "//skia",
       "//ui/events/ozone:events_ozone_evdev",
       "//ui/events/ozone:events_ozone_layout",
     ]
 
     public_configs = [ ":libgbm" ]
   }
 }