Add is_chromecast to GN build.

ui/ozone/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("//ui/ozone/ozone.gni")
 import("//testing/test.gni")
 
 # The list of platforms that will be built.
 ozone_platforms = []
 
@@ skipping 17 matching lines @@
   ozone_platforms += [ "caca" ]
   ozone_platform_deps += [ "platform/caca" ]
 }
 
 if (ozone_platform_gbm) {
   ozone_platforms += [ "gbm" ]
   ozone_platform_deps += [ "platform/drm:gbm" ]
   ozone_platform_test_deps += [ "platform/drm:gbm_unittests" ]
 }
 
+if (ozone_platform_cast) {
+  ozone_platforms += [ "cast" ]
+  ozone_platform_deps += [ "platform/cast" ]
+}
+
 platform_list_cc_file = "$target_gen_dir/platform_list.cc"
 platform_list_h_file = "$target_gen_dir/platform_list.h"
 platform_list_txt_file = "$target_gen_dir/platform_list.txt"
 constructor_list_cc_file = "$target_gen_dir/constructor_list.cc"
 
 # GYP version: ui/ozone/ozone.gyp:ozone_base
 component("ozone_base") {
   sources = [
     "public/cursor_factory_ozone.cc",
     "public/cursor_factory_ozone.h",
@@ skipping 130 matching lines @@
   sources = [
     "run_all_unittests.cc",
   ]
 
   deps = [
            "//base/test:test_support",
            "//testing/gtest",
            "//ui/gfx/geometry",
          ] + ozone_platform_test_deps
 }