[Sync] Move thread checking into the ModelSafeWorker interface.

components/browser_sync/profile_sync_test_util.cc

 // Copyright 2016 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.
 
 #include "components/browser_sync/profile_sync_test_util.h"
 
 #include <utility>
 
 #include "base/memory/ptr_util.h"
 #include "components/bookmarks/browser/bookmark_model.h"
@@ skipping 242 matching lines @@
   init_params.sync_client = std::move(sync_client);
   init_params.signin_wrapper =
       base::MakeUnique<SigninManagerWrapper>(signin_manager());
   init_params.oauth2_token_service = auth_service();
   init_params.network_time_update_callback =
       base::Bind(&EmptyNetworkTimeUpdate);
   init_params.base_directory = base::FilePath(FILE_PATH_LITERAL("dummyPath"));
   init_params.url_request_context = url_request_context();
   init_params.debug_identifier = "dummyDebugName";
   init_params.channel = version_info::Channel::UNKNOWN;
-  init_params.db_thread = db_thread_;
-  init_params.file_thread = base::ThreadTaskRunnerHandle::Get();
   init_params.blocking_pool = worker_pool_owner_.pool().get();
 
   return init_params;
 }
 
 }  // namespace browser_sync