[Sync] Replace typedef with using.

components/sync/engine/net/http_post_provider_factory.h

 // Copyright 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 COMPONENTS_SYNC_ENGINE_NET_HTTP_POST_PROVIDER_FACTORY_H_
 #define COMPONENTS_SYNC_ENGINE_NET_HTTP_POST_PROVIDER_FACTORY_H_
 
 #include <string>
 
 #include "base/callback.h"
 
 namespace net {
 class URLFetcher;
 }
 
 namespace syncer {
 
-typedef base::Callback<void(net::URLFetcher*)> BindToTrackerCallback;
+using BindToTrackerCallback = base::Callback<void(net::URLFetcher*)>;
 
 class HttpPostProviderInterface;
 
 // A factory to create HttpPostProviders to hide details about the
 // implementations and dependencies.
 // A factory instance itself should be owned by whomever uses it to create
 // HttpPostProviders.
 class HttpPostProviderFactory {
  public:
   virtual ~HttpPostProviderFactory() {}
 
   virtual void Init(const std::string& user_agent,
                     const BindToTrackerCallback& bind_to_tracker_callback) = 0;
 
   // Obtain a new HttpPostProviderInterface instance, owned by caller.
   virtual HttpPostProviderInterface* Create() = 0;
 
   // When the interface is no longer needed (ready to be cleaned up), clients
   // must call Destroy().
   // This allows actual HttpPostProvider subclass implementations to be
   // reference counted, which is useful if a particular implementation uses
   // multiple threads to serve network requests.
   virtual void Destroy(HttpPostProviderInterface* http) = 0;
 };
 
 }  // namespace syncer
 
 #endif  // COMPONENTS_SYNC_ENGINE_NET_HTTP_POST_PROVIDER_FACTORY_H_