[Sync] Replace typedef with using.

components/sync/model/attachments/attachment_service.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_ATTACHMENTS_ATTACHMENT_SERVICE_H_
 #define COMPONENTS_SYNC_MODEL_ATTACHMENTS_ATTACHMENT_SERVICE_H_
 
 #include <memory>
 
 #include "base/callback.h"
@@ skipping 15 matching lines @@
 // Destroying this object does not necessarily cancel outstanding async
 // operations. If you need cancel like semantics, use WeakPtr in the callbacks.
 class AttachmentService {
  public:
   // The result of a GetOrDownloadAttachments operation.
   enum GetOrDownloadResult {
     GET_SUCCESS,            // No error, all attachments returned.
     GET_UNSPECIFIED_ERROR,  // An unspecified error occurred.
   };
 
-  typedef base::Callback<void(const GetOrDownloadResult&,
-                              std::unique_ptr<AttachmentMap> attachments)>
-      GetOrDownloadCallback;
+  using GetOrDownloadCallback =
+      base::Callback<void(const GetOrDownloadResult&,
+                          std::unique_ptr<AttachmentMap> attachments)>;
 
   // An interface that embedder code implements to be notified about different
   // events that originate from AttachmentService.
   // This interface will be called from the same thread AttachmentService was
   // created and called.
   class Delegate {
    public:
     virtual ~Delegate() {}
 
     // Attachment is uploaded to server and attachment_id is updated with server
@@ skipping 30 matching lines @@
   //
   // A request to upload attachments does not persist across restarts of Chrome.
   //
   // Invokes OnAttachmentUploaded on the Delegate (if provided).
   virtual void UploadAttachments(const AttachmentIdList& attachment_ids) = 0;
 };
 
 }  // namespace syncer
 
 #endif  // COMPONENTS_SYNC_MODEL_ATTACHMENTS_ATTACHMENT_SERVICE_H_