cros: Remove usage of GaiaScreenHandler outside of login/webui.

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 786 matching lines @@
     "login/screens/enable_debugging_screen.h",
     "login/screens/enable_debugging_screen_view.h",
     "login/screens/error_screen.cc",
     "login/screens/error_screen.h",
     "login/screens/error_screen_view_delegate.h",
     "login/screens/eula_screen.cc",
     "login/screens/eula_screen.h",
     "login/screens/eula_view.h",
     "login/screens/gaia_screen.cc",
     "login/screens/gaia_screen.h",
+    "login/screens/gaia_view.h",
     "login/screens/hid_detection_screen.cc",
     "login/screens/hid_detection_screen.h",
     "login/screens/hid_detection_view.h",
     "login/screens/host_pairing_screen.cc",
     "login/screens/host_pairing_screen.h",
     "login/screens/host_pairing_screen_view.cc",
     "login/screens/host_pairing_screen_view.h",
     "login/screens/kiosk_autolaunch_screen.cc",
     "login/screens/kiosk_autolaunch_screen.h",
     "login/screens/kiosk_autolaunch_screen_view.h",
@@ skipping 958 matching lines @@
     "policy/proto/chrome_device_policy.proto",
     "policy/proto/install_attributes.proto",
   ]
 }
 
 proto_library("attestation_proto") {
   sources = [
     "attestation/attestation_key_payload.proto",
   ]
 }