[Sync] Refactor ModelSafeWorker::DoWorkAndWaitUntilDone() to avoid code duplication.

components/sync/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/buildflag_header.gni")
 import("//build/config/features.gni")
 import("//components/sync/protocol/protocol_sources.gni")
 import("//testing/test.gni")
 
 static_library("sync") {
@@ skipping 43 matching lines @@
     "base/ordinal.h",
     "base/passphrase_type.cc",
     "base/passphrase_type.h",
     "base/pref_names.cc",
     "base/pref_names.h",
     "base/progress_marker_map.cc",
     "base/progress_marker_map.h",
     "base/proto_value_ptr.h",
     "base/report_unrecoverable_error.cc",
     "base/report_unrecoverable_error.h",
-    "base/scoped_event_signal.cc",
-    "base/scoped_event_signal.h",
     "base/stop_source.h",
     "base/sync_features.cc",
     "base/sync_features.h",
     "base/sync_prefs.cc",
     "base/sync_prefs.h",
     "base/syncer_error.cc",
     "base/syncer_error.h",
     "base/system_encryptor.cc",
     "base/system_encryptor.h",
     "base/time.cc",
@@ skipping 761 matching lines @@
     "base/data_type_histogram_unittest.cc",
     "base/enum_set_unittest.cc",
     "base/get_session_name_unittest.cc",
     "base/hash_util_unittest.cc",
     "base/immutable_unittest.cc",
     "base/nigori_unittest.cc",
     "base/node_ordinal_unittest.cc",
     "base/ordinal_unittest.cc",
     "base/proto_value_ptr_unittest.cc",
     "base/protobuf_unittest.cc",
-    "base/scoped_event_signal_unittest.cc",
     "base/sync_prefs_unittest.cc",
     "base/system_encryptor_unittest.cc",
     "base/unique_position_unittest.cc",
     "base/weak_handle_unittest.cc",
     "device_info/device_count_metrics_provider_unittest.cc",
     "device_info/device_info_data_type_controller_unittest.cc",
     "device_info/device_info_sync_bridge_unittest.cc",
     "device_info/device_info_sync_service_unittest.cc",
     "device_info/device_info_util_unittest.cc",
     "device_info/local_device_info_provider_impl_unittest.cc",
@@ skipping 284 matching lines @@
     deps = [
       ":fake_server_jni",
       ":sync",
       ":test_support_fake_server",
       "//base",
       "//testing/gtest",
       "//url:url",
     ]
   }
 }