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

chrome/browser/downgrade/user_data_downgrade_browsertest.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 "base/files/file_util.h"
 #include "base/path_service.h"
 #include "base/strings/utf_string_conversions.h"
 #include "base/test/test_reg_util_win.h"
+#include "base/threading/sequenced_worker_pool.h"
 #include "base/version.h"
 #include "base/win/registry.h"
 #include "chrome/common/chrome_constants.h"
 #include "chrome/common/chrome_paths.h"
 #include "chrome/installer/util/browser_distribution.h"
 #include "chrome/installer/util/google_update_constants.h"
 #include "chrome/test/base/in_process_browser_test.h"
 #include "content/public/browser/browser_thread.h"
 
 namespace downgrade {
@@ skipping 104 matching lines @@
   ASSERT_TRUE(base::PathExists(other_file_));
 }
 
 // Verify the "Last Version" file won't be created for non-msi install.
 IN_PROC_BROWSER_TEST_F(UserDataDowngradeBrowserNoMSITest, Test) {
   ASSERT_FALSE(base::PathExists(last_version_file_path_));
   ASSERT_TRUE(base::PathExists(other_file_));
 }
 
 }  // namespace downgrade