Remove header dependencies from sequence_checker.h to sequenced_worker_pool.h

components/ntp_tiles/popular_sites_impl.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 "components/ntp_tiles/popular_sites_impl.h"
 
 #include <stddef.h>
 #include <utility>
 
 #include "base/bind.h"
 #include "base/command_line.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/threading/sequenced_worker_pool.h"
 #include "base/time/time.h"
 #include "base/values.h"
 #include "components/data_use_measurement/core/data_use_user_data.h"
 #include "components/google/core/browser/google_util.h"
 #include "components/ntp_tiles/constants.h"
 #include "components/ntp_tiles/pref_names.h"
 #include "components/ntp_tiles/switches.h"
 #include "components/pref_registry/pref_registry_syncable.h"
 #include "components/prefs/pref_service.h"
 #include "components/search_engines/search_engine_type.h"
@@ skipping 324 matching lines @@
     pending_url_ = GetPopularSitesURL(kPopularSitesDefaultCountryCode,
                                       kPopularSitesDefaultVersion);
     FetchPopularSites();
   } else {
     DLOG(WARNING) << "Download fallback site list failed";
     callback_.Run(false);
   }
 }
 
 }  // namespace ntp_tiles