[Ozone-DRI] Add display observer

ui/ozone/platform/dri/dri.gypi

 # 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.
 
 {
   'variables': {
     'internal_ozone_platform_deps': [
       'ozone_platform_dri',
     ],
     'internal_ozone_platform_unittest_deps': [
@@ skipping 20 matching lines @@
         '../gfx/gfx.gyp:gfx',
         '../gfx/gfx.gyp:gfx_geometry',
       ],
       'defines': [
         'OZONE_IMPLEMENTATION',
       ],
       '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_buffer.cc',
         'dri_buffer.h',
@@ skipping 66 matching lines @@
           'hardware_display_controller_unittest.cc',
           'hardware_display_plane_manager_unittest.cc',
           'screen_manager_unittest.cc',
           'test/mock_dri_wrapper.cc',
           'test/mock_dri_wrapper.h',
         ],
       },
     },
   ],
 }