Remove header dependencies from sequence_checker.h to sequenced_worker_pool.h

ios/chrome/browser/sync/ios_chrome_profile_sync_service_factory.cc

 // Copyright 2015 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 "ios/chrome/browser/sync/ios_chrome_profile_sync_service_factory.h"
 
 #include <utility>
 
 #include "base/memory/ptr_util.h"
 #include "base/memory/singleton.h"
+#include "base/threading/sequenced_worker_pool.h"
 #include "base/time/time.h"
 #include "components/browser_sync/profile_sync_service.h"
 #include "components/keyed_service/ios/browser_state_dependency_manager.h"
 #include "components/network_time/network_time_tracker.h"
 #include "components/signin/core/browser/profile_oauth2_token_service.h"
 #include "components/signin/core/browser/signin_manager.h"
 #include "components/sync/driver/signin_manager_wrapper.h"
 #include "components/sync/driver/startup_controller.h"
 #include "components/sync/driver/sync_util.h"
 #include "ios/chrome/browser/application_context.h"
@@ skipping 125 matching lines @@
       blocking_pool->GetSequencedTaskRunnerWithShutdownBehavior(
           blocking_pool->GetSequenceToken(),
           base::SequencedWorkerPool::SKIP_ON_SHUTDOWN);
 
   auto pss = base::MakeUnique<ProfileSyncService>(std::move(init_params));
 
   // Will also initialize the sync client.
   pss->Initialize();
   return std::move(pss);
 }