Add missing #include around sequenced_worker_pool.h in //chrome

chrome/browser/component_updater/sth_set_component_installer.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 "chrome/browser/component_updater/sth_set_component_installer.h"
 
 #include <utility>
 
 #include "base/bind.h"
 #include "base/files/file_enumerator.h"
 #include "base/files/file_path.h"
 #include "base/files/file_util.h"
 #include "base/json/json_reader.h"
 #include "base/logging.h"
 #include "base/path_service.h"
 #include "base/strings/string_number_conversions.h"
+#include "base/threading/sequenced_worker_pool.h"
 #include "base/values.h"
 #include "base/version.h"
 #include "chrome/browser/net/sth_distributor_provider.h"
 #include "components/component_updater/component_updater_paths.h"
 #include "content/public/browser/browser_thread.h"
 #include "crypto/sha2.h"
 #include "net/cert/ct_log_response_parser.h"
 #include "net/cert/signed_tree_head.h"
 #include "net/cert/sth_distributor.h"
 #include "net/cert/sth_observer.h"
@@ skipping 175 matching lines @@
 
   std::unique_ptr<ComponentInstallerTraits> traits(
       new STHSetComponentInstallerTraits(distributor));
   // |cus| will take ownership of |installer| during installer->Register(cus).
   DefaultComponentInstaller* installer =
       new DefaultComponentInstaller(std::move(traits));
   installer->Register(cus, base::Closure());
 }
 
 }  // namespace component_updater