ozone gbm: whitelist 3 DRM ioctl code for native GpuMemoryBuffer.

ui/ozone/ozone.gni

Index: ui/ozone/ozone.gni
diff --git a/ui/ozone/ozone.gni b/ui/ozone/ozone.gni
index e36b1d11b65612832445c62690c7f15de362e307..cb6f62ee28c7889697ebb5a4f9d743ea7969b9ad 100644
--- a/ui/ozone/ozone.gni
+++ b/ui/ozone/ozone.gni
@@ -7,6 +7,13 @@ import("//build/config/chromecast_build.gni")
 declare_args() {
   # Select platforms automatically. Turn this off for manual control.
   ozone_auto_platforms = true
+
+  # This enables memory-mapped access to accelerated graphics buffers via the
+  # VGEM ("virtual GEM") driver. This is currently only available on Chrome OS
+  # kernels and affects code in the GBM ozone platform.
+  # TODO(dshwang): remove this flag when all gbm hardware supports vgem map.
+  # crbug.com/519587
+  use_vgem_map = false
 }
 
 declare_args() {