Rename is_chromeos in chrome/src.

components/session_manager/core/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/features.gni")
+
 component("core") {
   sources = [
     "../session_manager_export.h",
     "session_manager.cc",
     "session_manager.h",
   ]
   deps = [
     "//base",
   ]
-  if (is_chromeos) {
+  if (use_cros_fe) {
     deps += [ "//chromeos" ]
   }
   defines = [ "SESSION_IMPLEMENTATION" ]
 }