Add SingleLogSource to system_logs sources

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 1331 matching lines @@
     "system_logs/dbus_log_source.cc",
     "system_logs/dbus_log_source.h",
     "system_logs/debug_daemon_log_source.cc",
     "system_logs/debug_daemon_log_source.h",
     "system_logs/debug_log_writer.cc",
     "system_logs/debug_log_writer.h",
     "system_logs/device_event_log_source.cc",
     "system_logs/device_event_log_source.h",
     "system_logs/lsb_release_log_source.cc",
     "system_logs/lsb_release_log_source.h",
+    "system_logs/single_log_source.cc",
+    "system_logs/single_log_source.h",
     "system_logs/touch_log_source.h",
     "system_logs/touch_log_source_ozone.cc",
     "system_logs/touch_log_source_x11.cc",
     "tether/tether_service.cc",
     "tether/tether_service.h",
     "tether/tether_service_factory.cc",
     "tether/tether_service_factory.h",
     "ui/accessibility_cursor_ring_layer.cc",
     "ui/accessibility_cursor_ring_layer.h",
     "ui/accessibility_focus_ring.cc",
@@ skipping 366 matching lines @@
     "settings/device_settings_service_unittest.cc",
     "settings/install_attributes_unittest.cc",
     "settings/scoped_cros_settings_test_helper.cc",
     "settings/scoped_cros_settings_test_helper.h",
     "settings/session_manager_operation_unittest.cc",
     "settings/shutdown_policy_handler_unittest.cc",
     "settings/stub_cros_settings_provider_unittest.cc",
     "status/data_promo_notification_unittest.cc",
     "system/automatic_reboot_manager_unittest.cc",
     "system/device_disabling_manager_unittest.cc",
+    "system_logs/single_log_source_unittest.cc",
     "ui/accessibility_focus_ring_controller_unittest.cc",
     "ui/idle_app_name_notification_view_unittest.cc",
     "ui/low_disk_notification_unittest.cc",
 
     # TODO(zturner): Enable this on Windows. See
     # BrowserWithTestWindowTest::SetUp() for a comment explaining why this is
     # broken.
     "../../common/extensions/api/file_browser_handlers/file_browser_handler_manifest_unittest.cc",
     "../../common/extensions/api/file_system_provider/file_system_provider_handler_unittest.cc",
     "../ui/views/frame/immersive_mode_controller_ash_unittest.cc",
@@ skipping 81 matching lines @@
     "policy/proto/chrome_device_policy.proto",
     "policy/proto/install_attributes.proto",
   ]
 }
 
 proto_library("attestation_proto") {
   sources = [
     "attestation/attestation_key_payload.proto",
   ]
 }