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 e307a352d578184fc4ba74e32c3a469e118c9d61..f1aeb08ac596dfc2cabc38551d38eddf9d8e80a6 100644
--- a/ui/ozone/ozone.gni
+++ b/ui/ozone/ozone.gni
@@ -5,6 +5,13 @@
 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() {