Convert //sync from scoped_ptr to std::unique_ptr

sync/internal_api/attachments/attachment_downloader.cc

Index: sync/internal_api/attachments/attachment_downloader.cc
diff --git a/sync/internal_api/attachments/attachment_downloader.cc b/sync/internal_api/attachments/attachment_downloader.cc
index c295e95cd8dfa9c84ae33da4ea558e59162ad10b..b46bb133534078f540976b86ce409f7f50726ee7 100644
--- a/sync/internal_api/attachments/attachment_downloader.cc
+++ b/sync/internal_api/attachments/attachment_downloader.cc
@@ -16,7 +16,7 @@ AttachmentDownloader::~AttachmentDownloader() {
 // Factory function for creating AttachmentDownloaderImpl.
 // It is introduced to avoid SYNC_EXPORT-ing AttachmentDownloaderImpl since it
 // inherits from OAuth2TokenService::Consumer which is not exported.
-scoped_ptr<AttachmentDownloader> AttachmentDownloader::Create(
+std::unique_ptr<AttachmentDownloader> AttachmentDownloader::Create(
     const GURL& sync_service_url,
     const scoped_refptr<net::URLRequestContextGetter>&
         url_request_context_getter,
@@ -26,7 +26,7 @@ scoped_ptr<AttachmentDownloader> AttachmentDownloader::Create(
         token_service_provider,
     const std::string& store_birthday,
     ModelType model_type) {
-  return scoped_ptr<AttachmentDownloader>(new AttachmentDownloaderImpl(
+  return std::unique_ptr<AttachmentDownloader>(new AttachmentDownloaderImpl(
       sync_service_url, url_request_context_getter, account_id, scopes,
       token_service_provider, store_birthday, model_type));
 }