Consolidate attachment URL construction.

sync/api/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 SYNC_API_ATTACHMENTS_ATTACHMENT_DOWNLOADER_H_
 #define SYNC_API_ATTACHMENTS_ATTACHMENT_DOWNLOADER_H_
 
 #include "base/callback.h"
 #include "base/memory/scoped_ptr.h"
 #include "google_apis/gaia/oauth2_token_service_request.h"
@@ skipping 23 matching lines @@
 
   // 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;
 
   // Create instance of AttachmentDownloaderImpl.
-  // |url_prefix| is the URL prefix (including trailing slash) to be used when
-  // downloading attachments.
+  // |sync_service_url| is the URL of the sync service.
   //
   // |url_request_context_getter| provides a URLRequestContext.
   //
   // |account_id| is the account id to use for downloads.
   //
   // |scopes| is the set of scopes to use for downloads.
   //
   // |token_service_provider| provides an OAuth2 token service.
   static scoped_ptr<AttachmentDownloader> Create(
-      const std::string& url_prefix,
+      const GURL& sync_service_url,
       const scoped_refptr<net::URLRequestContextGetter>&
           url_request_context_getter,
       const std::string& account_id,
       const OAuth2TokenService::ScopeSet scopes,
       scoped_ptr<OAuth2TokenServiceRequest::TokenServiceProvider>
           token_service_provider);
 };
 
 }  // namespace syncer
 
 #endif  // SYNC_API_ATTACHMENTS_ATTACHMENT_DOWNLOADER_H_