Rename is_chromeos in chrome/src.

chrome/third_party/chromevox/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.
 
-if (is_chromeos) {
+if (use_cros_fe) {
   import("//chrome/browser/resources/chromeos/chromevox/chromevox.gni")
 
   chromevox_out_dir = "$root_out_dir/resources/chromeos/chromevox"
 
   group("chromevox_third_party_resources") {
     deps = [
       ":chromevox_third_party_background_resources",
       ":chromevox_third_party_injected_resources",
     ]
   }
@@ skipping 12 matching lines @@
   copy("chromevox_third_party_injected_resources") {
     sources = [
       "chromevox/injected/mathjax.js",
       "chromevox/injected/mathjax_external_util.js",
     ]
     outputs = [
       "$chromevox_out_dir/chromevox/injected/{{source_file_part}}",
     ]
   }
 }