Use SequencedTaskRunner rather than SingledThreadedTaskRunner for passing io_task_runner

net/proxy/proxy_config_service_mac.h

 // 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.
 
 #ifndef NET_PROXY_PROXY_CONFIG_SERVICE_MAC_H_
 #define NET_PROXY_PROXY_CONFIG_SERVICE_MAC_H_
 
 #include <memory>
 
 #include "base/compiler_specific.h"
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #include "base/observer_list.h"
 #include "net/base/network_config_watcher_mac.h"
 #include "net/proxy/proxy_config.h"
 #include "net/proxy/proxy_config_service.h"
 
 namespace base {
-class SingleThreadTaskRunner;
+class SequencedTaskRunner;
 }  // namespace base
 
 namespace net {
 
 class ProxyConfigServiceMac : public ProxyConfigService {
  public:
   // Constructs a ProxyConfigService that watches the Mac OS system settings.
-  // This instance is expected to be operated and deleted on the same thread
-  // (however it may be constructed from a different thread).
+  // This instance is expected to be operated and deleted on the
+  // same sequenced task runner (however it may be constructed elsewhere).
   explicit ProxyConfigServiceMac(
-      const scoped_refptr<base::SingleThreadTaskRunner>& io_thread_task_runner);
+      const scoped_refptr<base::SequencedTaskRunner>& io_thread_task_runner);
   ~ProxyConfigServiceMac() override;
 
  public:
   // ProxyConfigService implementation:
   void AddObserver(Observer* observer) override;
   void RemoveObserver(Observer* observer) override;
   ConfigAvailability GetLatestProxyConfig(ProxyConfig* config) override;
 
  private:
   class Helper;
@@ skipping 26 matching lines @@
   std::unique_ptr<const NetworkConfigWatcherMac> config_watcher_;
 
   base::ObserverList<Observer> observers_;
 
   // Holds the last system proxy settings that we fetched.
   bool has_fetched_config_;
   ProxyConfig last_config_fetched_;
 
   scoped_refptr<Helper> helper_;
 
-  // The thread that we expect to be operated on.
-  const scoped_refptr<base::SingleThreadTaskRunner> io_thread_task_runner_;
+  // The task runner that |this| will be operated on.
+  const scoped_refptr<base::SequencedTaskRunner> io_thread_task_runner_;
 
   DISALLOW_COPY_AND_ASSIGN(ProxyConfigServiceMac);
 };
 
 }  // namespace net
 
 #endif  // NET_PROXY_PROXY_CONFIG_SERVICE_MAC_H_