Use SequencedTaskRunner rather than SingledThreadedTaskRunner for passing io_task_runner

net/proxy/proxy_config_service_linux.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_config_service_linux.h"
 
 #include <errno.h>
 #if defined(USE_GCONF)
 #include <gconf/gconf-client.h>
 #endif  // defined(USE_GCONF)
@@ skipping 1552 matching lines @@
 }
 
 ProxyConfigServiceLinux::Delegate::Delegate(
     std::unique_ptr<base::Environment> env_var_getter,
     SettingGetter* setting_getter)
     : env_var_getter_(std::move(env_var_getter)),
       setting_getter_(setting_getter) {}
 
 void ProxyConfigServiceLinux::Delegate::SetUpAndFetchInitialConfig(
     const scoped_refptr<base::SingleThreadTaskRunner>& glib_task_runner,
-    const scoped_refptr<base::SingleThreadTaskRunner>& io_task_runner) {
+    const scoped_refptr<base::SequencedTaskRunner>& io_task_runner) {
   // We should be running on the default glib main loop thread right
   // now. gconf can only be accessed from this thread.
   DCHECK(glib_task_runner->RunsTasksInCurrentSequence());
   glib_task_runner_ = glib_task_runner;
   io_task_runner_ = io_task_runner;
 
   // If we are passed a NULL |io_task_runner|, then don't set up proxy
   // setting change notifications. This should not be the usual case but is
   // intended to/ simplify test setups.
   if (!io_task_runner_.get())
@@ skipping 189 matching lines @@
 void ProxyConfigServiceLinux::RemoveObserver(Observer* observer) {
   delegate_->RemoveObserver(observer);
 }
 
 ProxyConfigService::ConfigAvailability
     ProxyConfigServiceLinux::GetLatestProxyConfig(ProxyConfig* config) {
   return delegate_->GetLatestProxyConfig(config);
 }
 
 }  // namespace net