Switch DRM platform to using a separate thread

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 27 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_gpu_platform_support_proxy.cc",
+    "gpu/drm_gpu_platform_support_proxy.h",
     "gpu/drm_surface.cc",
     "gpu/drm_surface.h",
     "gpu/drm_surface_factory.cc",
     "gpu/drm_surface_factory.h",
+    "gpu/drm_thread.cc",
+    "gpu/drm_thread.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/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/scanout_buffer.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",
@@ skipping 129 matching lines @@
     if (use_vgem_map) {
       defines += [ "USE_VGEM_MAP" ]
 
       sources += [
         "gpu/client_native_pixmap_vgem.cc",
         "gpu/client_native_pixmap_vgem.h",
       ]
     }
   }
 }