Add policy provider that would filter extensions/apps allowed on the

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("//media/media_options.gni")
 import("//printing/features/features.gni")
 import("//third_party/protobuf/proto_library.gni")
 
@@ skipping 379 matching lines @@
     "extensions/input_method_event_router.cc",
     "extensions/input_method_event_router.h",
     "extensions/install_limiter.cc",
     "extensions/install_limiter.h",
     "extensions/install_limiter_factory.cc",
     "extensions/install_limiter_factory.h",
     "extensions/launcher_search_provider.cc",
     "extensions/launcher_search_provider.h",
     "extensions/media_player_event_router.cc",
     "extensions/media_player_event_router.h",
+    "extensions/signin_screen_policy_provider.cc",
+    "extensions/signin_screen_policy_provider.h",
     "external_metrics.cc",
     "external_metrics.h",
     "external_protocol_dialog.cc",
     "external_protocol_dialog.h",
     "feedback_util.cc",
     "feedback_util.h",
     "file_manager/app_id.h",
     "file_manager/arc_file_tasks.cc",
     "file_manager/arc_file_tasks.h",
     "file_manager/file_browser_handlers.cc",
@@ skipping 992 matching lines @@
     "events/event_rewriter_unittest.cc",
     "events/keyboard_driven_event_rewriter_unittest.cc",
     "extensions/default_app_order_unittest.cc",
     "extensions/device_local_account_external_policy_loader_unittest.cc",
     "extensions/device_local_account_management_policy_provider_unittest.cc",
     "extensions/external_cache_unittest.cc",
     "extensions/file_manager/device_event_router_unittest.cc",
     "extensions/file_manager/job_event_router_unittest.cc",
     "extensions/gfx_utils_unittest.cc",
     "extensions/quick_unlock_private/quick_unlock_private_api_unittest.cc",
+    "extensions/signin_screen_policy_provider_unittest.cc",
     "extensions/wallpaper_private_api_unittest.cc",
     "external_metrics_unittest.cc",
     "file_manager/file_tasks_unittest.cc",
     "file_manager/file_watcher_unittest.cc",
     "file_manager/fileapi_util_unittest.cc",
     "file_manager/mount_test_util.cc",
     "file_manager/path_util_unittest.cc",
     "file_manager/url_util_unittest.cc",
     "file_manager/volume_manager_unittest.cc",
     "file_system_provider/fake_provided_file_system.cc",
@@ skipping 215 matching lines @@
     "policy/proto/chrome_device_policy.proto",
     "policy/proto/install_attributes.proto",
   ]
 }
 
 proto_library("attestation_proto") {
   sources = [
     "attestation/attestation_key_payload.proto",
   ]
 }