[Sync] Replace typedef with using.

components/sync/engine/attachments/attachment_downloader.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_ENGINE_ATTACHMENTS_ATTACHMENT_DOWNLOADER_H_
 #define COMPONENTS_SYNC_ENGINE_ATTACHMENTS_ATTACHMENT_DOWNLOADER_H_
 
 #include <memory>
 #include <string>
 
@@ skipping 12 matching lines @@
 class AttachmentDownloader {
  public:
   // The result of a DownloadAttachment operation.
   enum DownloadResult {
     DOWNLOAD_SUCCESS,            // No error, attachment was downloaded
                                  // successfully.
     DOWNLOAD_TRANSIENT_ERROR,    // A transient error occurred, try again later.
     DOWNLOAD_UNSPECIFIED_ERROR,  // An unspecified error occurred.
   };
 
-  typedef base::Callback<void(const DownloadResult&,
-                              std::unique_ptr<Attachment>)>
-      DownloadCallback;
+  using DownloadCallback =
+      base::Callback<void(const DownloadResult&, std::unique_ptr<Attachment>)>;
 
   virtual ~AttachmentDownloader();
 
   // Download attachment referred by |attachment_id| and invoke |callback| when
   // done.
   //
   // |callback| will receive a DownloadResult code and an Attachment object. If
   // DownloadResult is not DOWNLOAD_SUCCESS then attachment pointer is null.
   virtual void DownloadAttachment(const AttachmentId& attachment_id,
                                   const DownloadCallback& callback) = 0;
@@ skipping 21 matching lines @@
       const OAuth2TokenService::ScopeSet scopes,
       const scoped_refptr<OAuth2TokenServiceRequest::TokenServiceProvider>&
           token_service_provider,
       const std::string& store_birthday,
       ModelType model_type);
 };
 
 }  // namespace syncer
 
 #endif  // COMPONENTS_SYNC_ENGINE_ATTACHMENTS_ATTACHMENT_DOWNLOADER_H_