GN: Get os="chromeos" use_ozone=true to compile

media/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/android/config.gni")
 import("//build/config/arm.gni")
 import("//build/config/features.gni")
 import("//build/config/linux/pkg_config.gni")
 import("//build/config/ui.gni")
 import("//media/media_options.gni")
@@ skipping 30 matching lines @@
   }
 }
 
 if (use_ozone) {
   action("generate_ozone_constructor_list") {
     # Ozone platform objects are auto-generated using similar
     # patterns for naming and classes constructors. Here we build the
     # object MediaOzonePlatform.
     script = "../ui/ozone/generate_constructor_list.py"
 
-    platform_list_txt_file = "$target_gen_dir/ui/ozone/platform_list.txt"
-    constructor_list_cc_file = "$target_gen_dir/media/ozone/constructor_list.cc"
+    platform_list_txt_file = "$target_gen_dir/../ui/ozone/platform_list.txt"
+    constructor_list_cc_file = "$target_gen_dir/../media/ozone/constructor_list.cc"
 
     sources = [ platform_list_txt_file ]
     outputs = [ constructor_list_cc_file ]
     args = [
-      "--platform_list=$platform_list_txt_file",
-      "--output_cc=$constructor_list_cc_file",
+      "--platform_list=" + rebase_path(platform_list_txt_file, root_build_dir),
+      "--output_cc=" + rebase_path(constructor_list_cc_file, root_build_dir),
       "--namespace=media",
       "--typename=MediaOzonePlatform",
       "--include=\"media/ozone/media_ozone_platform.h\""
     ]
   }
 }
 
 component("media") {
   sources = [
     "cdm/aes_decryptor.cc",
@@ skipping 697 matching lines @@
     deps = [
       ":media",
       ":shared_memory_support",
       "//base",
       "//ui/gl",
       "//ui/gfx",
       "//ui/gfx/geometry",
     ]
   }
 }