[Sync] Fixing easy lint violations.

components/sync/core/attachments/attachment_downloader_impl.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_CORE_ATTACHMENTS_ATTACHMENT_DOWNLOADER_IMPL_H_
 #define COMPONENTS_SYNC_CORE_ATTACHMENTS_ATTACHMENT_DOWNLOADER_IMPL_H_
 
 #include <stdint.h>
 
+#include <memory>
 #include <string>
 #include <unordered_map>
 #include <vector>
 
 #include "base/gtest_prod_util.h"
 #include "base/macros.h"
 #include "base/threading/non_thread_safe.h"
 #include "components/sync/base/model_type.h"
 #include "components/sync/core/attachments/attachment_downloader.h"
 #include "google_apis/gaia/oauth2_token_service_request.h"
@@ skipping 104 matching lines @@
   StateList requests_waiting_for_access_token_;
 
   ModelType model_type_;
 
   DISALLOW_COPY_AND_ASSIGN(AttachmentDownloaderImpl);
 };
 
 }  // namespace syncer
 
 #endif  // COMPONENTS_SYNC_CORE_ATTACHMENTS_ATTACHMENT_DOWNLOADER_IMPL_H_