cros: More robust approach for setting login/lock webview background color.

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 857 matching lines @@
     "login/ui/login_web_dialog.h",
     "login/ui/models/user_board_model.cc",
     "login/ui/models/user_board_model.h",
     "login/ui/proxy_settings_dialog.cc",
     "login/ui/simple_web_view_dialog.cc",
     "login/ui/simple_web_view_dialog.h",
     "login/ui/user_adding_screen.cc",
     "login/ui/user_adding_screen.h",
     "login/ui/user_adding_screen_input_methods_controller.cc",
     "login/ui/user_adding_screen_input_methods_controller.h",
+    "login/ui/web_contents_set_background_color.cc",
+    "login/ui/web_contents_set_background_color.h",
     "login/ui/webui_login_display.cc",
     "login/ui/webui_login_display.h",
     "login/ui/webui_login_view.cc",
     "login/ui/webui_login_view.h",
     "login/user_flow.cc",
     "login/user_flow.h",
     "login/users/affiliation.cc",
     "login/users/affiliation.h",
     "login/users/avatar/user_image_loader.cc",
     "login/users/avatar/user_image_loader.h",
@@ skipping 770 matching lines @@
     "policy/proto/chrome_device_policy.proto",
     "policy/proto/install_attributes.proto",
   ]
 }
 
 proto_library("attestation_proto") {
   sources = [
     "attestation/attestation_key_payload.proto",
   ]
 }