Use SequencedTaskRunner rather than SingledThreadedTaskRunner for passing io_task_runner

net/proxy/proxy_service.cc

 // Copyright (c) 2012 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 "net/proxy/proxy_service.h"
 
 #include <algorithm>
 #include <cmath>
 #include <utility>
 
@@ skipping 1505 matching lines @@
 
 void ProxyService::ForceReloadProxyConfig() {
   DCHECK_CALLED_ON_VALID_THREAD(thread_checker_);
   ResetProxyConfig(false);
   ApplyProxyConfigIfAvailable();
 }
 
 // static
 std::unique_ptr<ProxyConfigService>
 ProxyService::CreateSystemProxyConfigService(
-    const scoped_refptr<base::SingleThreadTaskRunner>& io_task_runner) {
+    const scoped_refptr<base::SequencedTaskRunner>& io_task_runner) {
 #if defined(OS_WIN)
   return base::MakeUnique<ProxyConfigServiceWin>();
 #elif defined(OS_IOS)
   return base::MakeUnique<ProxyConfigServiceIOS>();
 #elif defined(OS_MACOSX)
   return base::MakeUnique<ProxyConfigServiceMac>(io_task_runner);
 #elif defined(OS_CHROMEOS)
   LOG(ERROR) << "ProxyConfigService for ChromeOS should be created in "
              << "profile_io_data.cc::CreateProxyConfigService and this should "
              << "be used only for examples.";
@@ skipping 134 matching lines @@
   State previous_state = ResetProxyConfig(false);
   if (previous_state != STATE_NONE)
     ApplyProxyConfigIfAvailable();
 }
 
 void ProxyService::OnDNSChanged() {
   OnIPAddressChanged();
 }
 
 }  // namespace net