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

chrome/browser/downgrade/user_data_downgrade.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/downgrade/user_data_downgrade.h"
 
 #include <string>
 
 #include "base/bind.h"
 #include "base/command_line.h"
 #include "base/files/file_enumerator.h"
 #include "base/files/file_path.h"
 #include "base/files/file_util.h"
 #include "base/path_service.h"
 #include "base/strings/string_util.h"
 #include "base/strings/stringprintf.h"
 #include "base/strings/utf_string_conversions.h"
+#include "base/threading/sequenced_worker_pool.h"
 #include "base/time/time.h"
 #include "base/version.h"
 #include "base/win/registry.h"
 #include "chrome/browser/policy/policy_path_parser.h"
 #include "chrome/common/chrome_constants.h"
 #include "chrome/common/chrome_paths.h"
 #include "chrome/common/chrome_switches.h"
 #include "chrome/common/chrome_version.h"
 #include "chrome/installer/util/google_update_constants.h"
 #include "chrome/installer/util/install_util.h"
@@ skipping 157 matching lines @@
          key.Open((install_level == SYSTEM_INSTALL) ? HKEY_LOCAL_MACHINE
                                                     : HKEY_CURRENT_USER,
                   BrowserDistribution::GetDistribution()->GetStateKey().c_str(),
                   KEY_QUERY_VALUE | KEY_WOW64_32KEY) == ERROR_SUCCESS &&
          key.ReadValueDW(google_update::kRegMSIField, &is_msi) ==
              ERROR_SUCCESS &&
          is_msi != 0;
 }
 
 }  // namespace downgrade