Remove the dependence on BrowserThread::FILE for

components/proxy_config/ios/proxy_service_factory.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/proxy_config/ios/proxy_service_factory.h"
 
 #include <utility>
 
 #include "base/memory/ptr_util.h"
 #include "components/proxy_config/pref_proxy_config_tracker_impl.h"
 #include "ios/web/public/web_thread.h"
 #include "net/proxy/proxy_config_service.h"
 #include "net/proxy/proxy_service.h"
 
 // static
 std::unique_ptr<net::ProxyConfigService>
 ProxyServiceFactory::CreateProxyConfigService(PrefProxyConfigTracker* tracker) {
   std::unique_ptr<net::ProxyConfigService> base_service(
       net::ProxyService::CreateSystemProxyConfigService(
-          web::WebThread::GetTaskRunnerForThread(web::WebThread::IO),
-          web::WebThread::GetTaskRunnerForThread(web::WebThread::FILE)));
+          web::WebThread::GetTaskRunnerForThread(web::WebThread::IO)));
   return tracker->CreateTrackingProxyConfigService(std::move(base_service));
 }
 
 // static
 std::unique_ptr<PrefProxyConfigTracker>
 ProxyServiceFactory::CreatePrefProxyConfigTrackerOfProfile(
     PrefService* browser_state_prefs,
     PrefService* local_state_prefs) {
   return base::MakeUnique<PrefProxyConfigTrackerImpl>(
       browser_state_prefs,
@@ skipping 16 matching lines @@
     net::NetworkDelegate* network_delegate,
     std::unique_ptr<net::ProxyConfigService> proxy_config_service,
     bool quick_check_enabled) {
   DCHECK_CURRENTLY_ON(web::WebThread::IO);
   std::unique_ptr<net::ProxyService> proxy_service(
       net::ProxyService::CreateUsingSystemProxyResolver(
           std::move(proxy_config_service), net_log));
   proxy_service->set_quick_check_enabled(quick_check_enabled);
   return proxy_service;
 }