Use SequencedTaskRunner rather than SingledThreadedTaskRunner for passing io_task_runner

net/proxy/proxy_config_service_linux.cc

Index: net/proxy/proxy_config_service_linux.cc
diff --git a/net/proxy/proxy_config_service_linux.cc b/net/proxy/proxy_config_service_linux.cc
index c2ae1a8a3985911b6924a5593812a3f347143ea9..bf852420a231baa438bef167a2100a844222286f 100644
--- a/net/proxy/proxy_config_service_linux.cc
+++ b/net/proxy/proxy_config_service_linux.cc
@@ -1570,7 +1570,7 @@ ProxyConfigServiceLinux::Delegate::Delegate(
 
 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());