[Sync] Replace typedef with using.

components/sync/model_impl/attachments/task_queue.h

 // Copyright 2014 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_MODEL_IMPL_ATTACHMENTS_TASK_QUEUE_H_
 #define COMPONENTS_SYNC_MODEL_IMPL_ATTACHMENTS_TASK_QUEUE_H_
 
 #include <stddef.h>
 
 #include <deque>
@@ skipping 58 matching lines @@
 // }
 //
 template <typename T>
 class TaskQueue : base::NonThreadSafe {
  public:
   // A callback provided by users of the TaskQueue to handle tasks.
   //
   // This callback is invoked by the queue with a task to be handled.  The
   // callee is expected to (eventually) call |MarkAsSucceeded|, |MarkAsFailed|,
   // or |Cancel| to signify completion of the task.
-  typedef base::Callback<void(const T&)> HandleTaskCallback;
+  using HandleTaskCallback = base::Callback<void(const T&)>;
 
   // Construct a TaskQueue.
   //
   // |callback| the callback to be invoked for handling tasks.
   //
   // |initial_backoff_delay| the initial amount of time the queue will wait
   // before dispatching tasks after a failed task (see |MarkAsFailed|).  May be
   // zero.  Subsequent failures will increase the delay up to
   // |max_backoff_delay|.
   //
@@ skipping 188 matching lines @@
 }
 
 template <typename T>
 bool TaskQueue<T>::ShouldDispatch() {
   return num_in_progress_ < kMaxConcurrentTasks && !queue_.empty();
 }
 
 }  // namespace syncer
 
 #endif  // COMPONENTS_SYNC_MODEL_IMPL_ATTACHMENTS_TASK_QUEUE_H_