Convert Ozone GL OSMesa implementation.

ui/ozone/common/BUILD.gn

 # Copyright 2016 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/ui.gni")
 
 assert(use_ozone)
 
 source_set("common") {
   sources = [
     "display_mode_proxy.cc",
     "display_mode_proxy.h",
     "display_snapshot_proxy.cc",
     "display_snapshot_proxy.h",
     "egl_util.cc",
     "egl_util.h",
     "gl_ozone_egl.cc",
     "gl_ozone_egl.h",
+    "gl_ozone_osmesa.cc",
+    "gl_ozone_osmesa.h",
     "gpu/ozone_gpu_message_generator.cc",
     "gpu/ozone_gpu_message_generator.h",
     "gpu/ozone_gpu_message_params.cc",
     "gpu/ozone_gpu_message_params.h",
     "gpu/ozone_gpu_messages.h",
     "stub_overlay_manager.cc",
     "stub_overlay_manager.h",
   ]
 
   public_deps = [
     "//ui/ozone:ozone_base",
   ]
 
   deps = [
     "//ui/gl",
   ]
 
   visibility = [ "//ui/ozone/platform/*" ]
 }