Expand Chrome OS ARC support to create one tree source per package

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 1521 matching lines @@
     "../metrics/chromeos_metrics_provider_unittest.cc",
     "../metrics/leak_detector/leak_detector_controller_unittest.cc",
     "../metrics/perf/cpu_identity_unittest.cc",
     "../metrics/perf/random_selector_unittest.cc",
     "../notifications/login_state_notification_blocker_chromeos_unittest.cc",
     "../policy/default_geolocation_policy_handler_unittest.cc",
     "../ui/browser_finder_chromeos_unittest.cc",
     "accessibility/magnification_manager_unittest.cc",
     "accessibility/select_to_speak_event_handler_unittest.cc",
     "accessibility/spoken_feedback_event_rewriter_unittest.cc",
+    "arc/accessibility/arc_accessibility_helper_bridge_unittest.cc",
     "arc/arc_play_store_enabled_preference_handler_unittest.cc",
     "arc/arc_session_manager_unittest.cc",
     "arc/arc_util_unittest.cc",
     "arc/downloads_watcher/arc_downloads_watcher_service_unittest.cc",
     "arc/extensions/arc_support_message_host_unittest.cc",
     "arc/fileapi/arc_content_file_system_async_file_util_unittest.cc",
     "arc/fileapi/arc_content_file_system_file_stream_reader_unittest.cc",
     "arc/fileapi/arc_content_file_system_url_util_unittest.cc",
     "arc/fileapi/arc_documents_provider_root_unittest.cc",
     "arc/fileapi/arc_documents_provider_util_unittest.cc",
@@ skipping 274 matching lines @@
     "policy/proto/chrome_device_policy.proto",
     "policy/proto/install_attributes.proto",
   ]
 }
 
 proto_library("attestation_proto") {
   sources = [
     "attestation/attestation_key_payload.proto",
   ]
 }