[Sync] Replace typedef with using.

components/sync/engine_impl/uss_migrator.h

 // Copyright 2016 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_IMPL_USS_MIGRATOR_H_
 #define COMPONENTS_SYNC_ENGINE_IMPL_USS_MIGRATOR_H_
 
 #include "base/callback.h"
 #include "components/sync/base/model_type.h"
 
 namespace syncer {
 
 class ModelTypeWorker;
 struct UserShare;
 
-typedef base::Callback<bool(ModelType, UserShare*, ModelTypeWorker*)>
-    UssMigrator;
+using UssMigrator =
+    base::Callback<bool(ModelType, UserShare*, ModelTypeWorker*)>;
 
 // Pulls all the data for |type| out of the directory and sends it to |worker|
 // as the result of an initial GetUpdates. Returns whether migration succeeded.
 bool MigrateDirectoryData(ModelType type,
                           UserShare* user_share,
                           ModelTypeWorker* worker);
 
 // A version of the above with |batch_size| as a parameter so it can be lowered
 // for unit testing.
 bool MigrateDirectoryDataWithBatchSize(ModelType type,
                                        UserShare* user_share,
                                        ModelTypeWorker* worker,
                                        int batch_size);
 
 }  // namespace syncer
 
 #endif  // COMPONENTS_SYNC_ENGINE_IMPL_USS_MIGRATOR_H_