Add GN build for parts of gpu and ozone.

ui/ozone/ozone.gni

+# 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/ui.gni")
+
+if (use_ozone) {
+  # Enable built-in ozone platforms if ozone is enabled.
+  ozone_platform_caca = false
+  ozone_platform_dri = true
+  ozone_platform_ozonex = false
+  ozone_platform_test = true
+} else {
+  ozone_platform_caca = false
+  ozone_platform_dri = false
+  ozone_platform_ozonex = false
+  ozone_platform_test = false
+}