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

ios/chrome/browser/ntp_tiles/ios_popular_sites_factory.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 "ios/chrome/browser/ntp_tiles/ios_popular_sites_factory.h"
 
 #include "base/bind.h"
 #include "base/files/file_path.h"
 #include "base/memory/ptr_util.h"
 #include "base/path_service.h"
-#include "base/threading/sequenced_worker_pool.h"
 #include "components/ntp_tiles/json_unsafe_parser.h"
 #include "components/ntp_tiles/popular_sites_impl.h"
 #include "ios/chrome/browser/application_context.h"
 #include "ios/chrome/browser/browser_state/chrome_browser_state.h"
 #include "ios/chrome/browser/chrome_paths.h"
 #include "ios/chrome/browser/search_engines/template_url_service_factory.h"
 #include "ios/web/public/web_thread.h"
 
 std::unique_ptr<ntp_tiles::PopularSites>
 IOSPopularSitesFactory::NewForBrowserState(
     ios::ChromeBrowserState* browser_state) {
   base::FilePath popular_sites_path;
   base::PathService::Get(ios::DIR_USER_DATA, &popular_sites_path);
   return base::MakeUnique<ntp_tiles::PopularSitesImpl>(
       web::WebThread::GetBlockingPool(), browser_state->GetPrefs(),
       ios::TemplateURLServiceFactory::GetForBrowserState(browser_state),
       GetApplicationContext()->GetVariationsService(),
       browser_state->GetRequestContext(), popular_sites_path,
       base::Bind(ntp_tiles::JsonUnsafeParser::Parse));
 }