ozone: Implement zero/one-copy texture for Ozone GBM.

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
+
+  # TODO(dshwang): remove this flag when all gbm hardwares support vgem map.
+  ozone_use_vgem_map = false

[reveman, 2015/08/07 17:59:44]

nit: s/hardwares/hardware/

can you create a bug?

ozone_use_vgem enough?

however, I'm still a bit confused about this. is the idea that we define this
when we know if hardware supports vgem? can we know that at compile time? if
not, why not include vgem_drm.h in third_party and remove this compile time
setting? both compile time and run time checking seems unnecessary..

[dshwang, 2015/08/11 17:44:56]

good concern. I remove run time checking. It's decided in compile time like
|use_mesa_platform_null|
Even if a hardware support vgem, it's possible for the hardware to not support
vgem map. e.g. ARM
So I name it as ozone_use_vgem_map to avoid confusion. for example, currently
ARM chromeos maintainer should not enable it.
I think only certain IA chromebook will enable this compile flag. Haswell and
Skylake are the first target.

I create crbug.com/519587 to remove this flag in the future.

 }
 
 pkg_config("libdrm") {
   packages = [ "libdrm" ]
 }
 
 source_set("drm_common") {
   sources = [
     "common/client_native_pixmap_factory_drm.cc",
     "common/client_native_pixmap_factory_drm.h",
@@ skipping 169 matching lines @@
     ]
 
     public_configs = [
       ":libgbm",
       "//third_party/khronos:khronos_headers",
     ]
 
     if (use_mesa_platform_null) {
       defines += [ "USE_MESA_PLATFORM_NULL" ]
     }
+
+    if (ozone_use_vgem_map) {
+      defines += [ "OZONE_USE_VGEM_MAP" ]
+
+      sources = [
+        "gpu/client_native_pixmap_vgem.cc",
+        "gpu/client_native_pixmap_vgem.h",
+      ]
+    }
   }
 }