cros: Move BaseScreenDelegate::ExitCodes into separate file, ScreenExitCode.

chrome/browser/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/features.gni")
 import("//build/config/ui.gni")
 import("//extensions/features/features.gni")
 import("//media/media_options.gni")
 import("//printing/features/features.gni")
 import("//third_party/protobuf/proto_library.gni")
@@ skipping 810 matching lines @@
     "login/screens/model_view_channel.h",
     "login/screens/network_error.cc",
     "login/screens/network_error.h",
     "login/screens/network_error_view.h",
     "login/screens/network_screen.cc",
     "login/screens/network_screen.h",
     "login/screens/network_view.h",
     "login/screens/reset_screen.cc",
     "login/screens/reset_screen.h",
     "login/screens/reset_view.h",
+    "login/screens/screen_exit_code.cc",
+    "login/screens/screen_exit_code.h",
     "login/screens/screen_flow.h",
     "login/screens/terms_of_service_screen.cc",
     "login/screens/terms_of_service_screen.h",
     "login/screens/terms_of_service_screen_view.h",
     "login/screens/update_screen.cc",
     "login/screens/update_screen.h",
     "login/screens/update_view.h",
     "login/screens/user_image_screen.cc",
     "login/screens/user_image_screen.h",
     "login/screens/user_selection_screen.cc",
@@ skipping 935 matching lines @@
     "policy/proto/chrome_device_policy.proto",
     "policy/proto/install_attributes.proto",
   ]
 }
 
 proto_library("attestation_proto") {
   sources = [
     "attestation/attestation_key_payload.proto",
   ]
 }