Switch DRM platform to using a separate thread

ui/ozone/platform/drm/BUILD.gn

Index: ui/ozone/platform/drm/BUILD.gn
diff --git a/ui/ozone/platform/drm/BUILD.gn b/ui/ozone/platform/drm/BUILD.gn
index 78d332bcfb2f6acc6f7abe6a6c0204e67be6724c..00fca46c22263ab5906099b23915f0622fcdeab6 100644
--- a/ui/ozone/platform/drm/BUILD.gn
+++ b/ui/ozone/platform/drm/BUILD.gn
@@ -45,14 +45,20 @@ source_set("drm_common") {
     "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",
@@ -65,6 +71,8 @@ source_set("drm_common") {
     "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",