[Sync] Move attachments code out of core/.

components/sync/core_impl/attachments/attachment_downloader.cc

-// 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.
-
-#include "components/sync/core/attachments/attachment_downloader.h"
-
-#include "components/sync/core/attachments/attachment_downloader_impl.h"
-
-namespace syncer {
-
-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.
-std::unique_ptr<AttachmentDownloader> AttachmentDownloader::Create(
-    const GURL& sync_service_url,
-    const scoped_refptr<net::URLRequestContextGetter>&
-        url_request_context_getter,
-    const std::string& account_id,
-    const OAuth2TokenService::ScopeSet scopes,
-    const scoped_refptr<OAuth2TokenServiceRequest::TokenServiceProvider>&
-        token_service_provider,
-    const std::string& store_birthday,
-    ModelType model_type) {
-  return std::unique_ptr<AttachmentDownloader>(new AttachmentDownloaderImpl(
-      sync_service_url, url_request_context_getter, account_id, scopes,
-      token_service_provider, store_birthday, model_type));
-}
-
-}  // namespace syncer