Rename is_chromeos in chrome/src.

chrome/common/variations/BUILD.gn

 # Copyright 2015 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/features.gni")
+
 action("fieldtrial_testing_config_action") {
   visibility = [ ":fieldtrial_testing_config" ]
   script = "//tools/variations/fieldtrial_to_struct.py"
 
   if (is_win) {
     source = "//testing/variations/fieldtrial_testing_config_win.json"
   }
   if (is_mac) {
     source = "//testing/variations/fieldtrial_testing_config_mac.json"
   }
   if (is_linux) {
     source = "//testing/variations/fieldtrial_testing_config_linux.json"
   }
-  if (is_chromeos) {
+  if (use_cros_fe) {
     source = "//testing/variations/fieldtrial_testing_config_chromeos.json"
   }
   if (is_android) {
     source = "//testing/variations/fieldtrial_testing_config_android.json"
   }
   if (is_ios) {
     source = "//testing/variations/fieldtrial_testing_config_ios.json"
   }
 
   inputs = [
@@ skipping 17 matching lines @@
     "--output=$out_name",
   ]
 }
 
 source_set("fieldtrial_testing_config") {
   sources = get_target_outputs(":fieldtrial_testing_config_action")
   deps = [
     ":fieldtrial_testing_config_action",
   ]
 }