Remove unused base/threading/worker_pool.h includes.

components/cronet/ios/cronet_environment.mm

 // 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 "components/cronet/ios/cronet_environment.h"
 
 #include <utility>
 
 #include "base/at_exit.h"
 #include "base/atomicops.h"
 #include "base/command_line.h"
 #include "base/feature_list.h"
 #include "base/files/file_path.h"
 #include "base/files/file_util.h"
 #include "base/files/scoped_file.h"
 #include "base/json/json_writer.h"
 #include "base/mac/bind_objc_block.h"
 #include "base/mac/foundation_util.h"
 #include "base/macros.h"
 #include "base/memory/ptr_util.h"
 #include "base/metrics/statistics_recorder.h"
 #include "base/path_service.h"
 #include "base/single_thread_task_runner.h"
 #include "base/synchronization/waitable_event.h"
 #include "base/task_scheduler/task_scheduler.h"
-#include "base/threading/worker_pool.h"
 #include "components/cronet/histogram_manager.h"
 #include "components/cronet/ios/version.h"
 #include "components/prefs/json_pref_store.h"
 #include "components/prefs/pref_filter.h"
 #include "ios/net/cookies/cookie_store_ios.h"
 #include "ios/web/public/user_agent.h"
 #include "net/base/network_change_notifier.h"
 #include "net/cert/cert_verifier.h"
 #include "net/dns/host_resolver.h"
 #include "net/dns/mapped_host_resolver.h"
@@ skipping 333 matching lines @@
   event->Signal();
 }
 
 std::string CronetEnvironment::getDefaultQuicUserAgentId() const {
   return base::SysNSStringToUTF8([[NSBundle mainBundle]
              objectForInfoDictionaryKey:@"CFBundleDisplayName"]) +
          " Cronet/" + CRONET_VERSION;
 }
 
 }  // namespace cronet