is_chromeos assertion for GN/ChromeOS

chromeos/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/allocator.gni")
 import("//build/config/ui.gni")
 import("//third_party/protobuf/proto_library.gni")
 
+assert(is_chromeos, "Non-ChromeOS builds must not depend on //chromeos")
+
 gypi_values = exec_script(
     "//build/gypi_to_gn.py",
     [ rebase_path("chromeos.gyp") ],
     "scope",
     [ "chromeos.gyp" ])
 
 component("chromeos") {
   configs += [
     "//build/config/linux:dbus",
     "//net/third_party/nss/ssl:ssl_config",
@@ skipping 165 matching lines @@
   proto_out_dir = "chromeos/dbus/cryptohome"
 }
 
 proto_library("cryptohome_signkey_proto") {
   sources = [
     "//third_party/cros_system_api/dbus/cryptohome/signed_secret.proto",
   ]
 
   proto_out_dir = "chromeos/cryptohome"
 }