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 hardware supports vgem map.
+  # crbug.com/519587
+  use_vgem_map = false
 }
 
 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 (use_vgem_map) {
+      defines += [ "USE_VGEM_MAP" ]
+
+      sources = [
+        "gpu/client_native_pixmap_vgem.cc",
+        "gpu/client_native_pixmap_vgem.h",
+      ]
+    }
   }
 }