Revert of Remove header dependencies from sequence_checker.h to sequenced_worker_pool.h

chrome/browser/sync_file_system/drive_backend/register_app_task_unittest.cc

 // Copyright 2013 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 "chrome/browser/sync_file_system/drive_backend/register_app_task.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <utility>
 #include <vector>
 
 #include "base/files/scoped_temp_dir.h"
 #include "base/format_macros.h"
 #include "base/macros.h"
 #include "base/memory/ptr_util.h"
 #include "base/run_loop.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/strings/stringprintf.h"
-#include "base/threading/sequenced_worker_pool.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "chrome/browser/sync_file_system/drive_backend/drive_backend_constants.h"
 #include "chrome/browser/sync_file_system/drive_backend/drive_backend_util.h"
 #include "chrome/browser/sync_file_system/drive_backend/fake_drive_service_helper.h"
 #include "chrome/browser/sync_file_system/drive_backend/leveldb_wrapper.h"
 #include "chrome/browser/sync_file_system/drive_backend/metadata_database.h"
 #include "chrome/browser/sync_file_system/drive_backend/metadata_database.pb.h"
 #include "chrome/browser/sync_file_system/drive_backend/sync_engine_context.h"
 #include "chrome/browser/sync_file_system/sync_file_system_test_util.h"
 #include "components/drive/drive_uploader.h"
@@ skipping 305 matching lines @@
 
   CreateMetadataDatabase(std::move(db));
   RunRegisterAppTask(kAppID);
 
   EXPECT_EQ(1u, CountRegisteredAppRoot());
   EXPECT_TRUE(IsAppRegistered(kAppID));
 }
 
 }  // namespace drive_backend
 }  // namespace sync_file_system