Preliminary atomic patch

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 996614413cf2fdcafe86be991708e41a4f3bf395..887f5914e0b7643cd93389538f335277954a7435 100644
--- a/ui/ozone/platform/drm/BUILD.gn
+++ b/ui/ozone/platform/drm/BUILD.gn
@@ -7,6 +7,7 @@ import("//ui/ozone/ozone.gni")
 
 declare_args() {
   use_mesa_platform_null = false
+  use_drm_atomic = false
 }
 
 pkg_config("libdrm") {
@@ -82,6 +83,16 @@ source_set("drm_common") {
 
   defines = [ "OZONE_IMPLEMENTATION" ]
 
+  if (use_drm_atomic) {
+    defines += [ "USE_DRM_ATOMIC" ]
+    sources += [
+      "gpu/hardware_display_plane_atomic.cc",
+      "gpu/hardware_display_plane_atomic.h",
+      "gpu/hardware_display_plane_manager_atomic.cc",
+      "gpu/hardware_display_plane_manager_atomic.h",
+    ]
+  }
+
   deps = [
     "//base",
     "//skia",