Switch DRM platform to using a separate thread

ui/ozone/platform/drm/gbm.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_gbm',
     ],
     'internal_ozone_platform_unittest_deps': [
@@ skipping 54 matching lines @@
         'gpu/drm_device_generator.cc',
         'gpu/drm_device_generator.h',
         'gpu/drm_device_manager.cc',
         'gpu/drm_device_manager.h',
         'gpu/drm_display.cc',
         'gpu/drm_display.h',
         'gpu/drm_gpu_display_manager.cc',
         'gpu/drm_gpu_display_manager.h',
         'gpu/drm_gpu_platform_support.cc',
         'gpu/drm_gpu_platform_support.h',
+        'gpu/drm_thread.cc',
+        'gpu/drm_thread.h',
+        'gpu/drm_thread_message_proxy.cc',
+        'gpu/drm_thread_message_proxy.h',
+        'gpu/drm_thread_proxy.cc',
+        'gpu/drm_thread_proxy.h',
         'gpu/drm_vsync_provider.cc',
         'gpu/drm_vsync_provider.h',
         'gpu/drm_window.cc',
         'gpu/drm_window.h',
+        'gpu/drm_window_proxy.cc',
+        'gpu/drm_window_proxy.h',
         'gpu/gbm_buffer.cc',
         'gpu/gbm_buffer.h',
         'gpu/gbm_buffer_base.cc',
         'gpu/gbm_buffer_base.h',
         'gpu/gbm_device.cc',
         'gpu/gbm_device.h',
         'gpu/gbm_surface_factory.cc',
         'gpu/gbm_surface_factory.h',
         'gpu/gbm_surfaceless.cc',
         'gpu/gbm_surfaceless.h',
         'gpu/hardware_display_controller.cc',
         'gpu/hardware_display_controller.h',
         'gpu/hardware_display_plane.cc',
         'gpu/hardware_display_plane.h',
         'gpu/hardware_display_plane_manager.cc',
         'gpu/hardware_display_plane_manager.h',
         'gpu/hardware_display_plane_manager_legacy.cc',
         'gpu/hardware_display_plane_manager_legacy.h',
         'gpu/overlay_plane.cc',
         'gpu/overlay_plane.h',
         'gpu/page_flip_request.cc',
         'gpu/page_flip_request.h',
+        'gpu/proxy_helpers.cc',
+        'gpu/proxy_helpers.h',
         'gpu/screen_manager.cc',
         'gpu/screen_manager.h',
         'host/channel_observer.h',
         'host/drm_cursor.cc',
         'host/drm_cursor.h',
         'host/drm_device_handle.cc',
         'host/drm_device_handle.h',
         'host/drm_display_host.cc',
         'host/drm_display_host.h',
         'host/drm_display_host_manager.cc',
@@ skipping 55 matching lines @@
           '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',
         ],
       },
     },
   ],
 }