Use the user's preferred downloads directory for creating the initial download file.

content/browser/download/download_file_impl.cc

 // Copyright (c) 2012 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 "content/browser/download/download_file_impl.h"
 
 #include <string>
 
 #include "base/bind.h"
 #include "base/file_util.h"
@@ skipping 17 matching lines @@
 const int kMaxTimeBlockingFileThreadMs = 1000;
 
 DownloadFileImpl::DownloadFileImpl(
     const DownloadCreateInfo* info,
     scoped_ptr<content::ByteStreamReader> stream,
     DownloadRequestHandleInterface* request_handle,
     scoped_refptr<DownloadManager> download_manager,
     bool calculate_hash,
     scoped_ptr<content::PowerSaveBlocker> power_save_blocker,
     const net::BoundNetLog& bound_net_log)
-        : file_(info->save_info.file_path,
+        : file_(info->default_download_directory,
+                info->save_info.file_path,
                 info->url(),
                 info->referrer_url,
                 info->received_bytes,
                 calculate_hash,
                 info->save_info.hash_state,
                 info->save_info.file_stream,
                 bound_net_log),
           stream_reader_(stream.Pass()),
           id_(info->download_id),
           request_handle_(request_handle),
@@ skipping 245 matching lines @@
   }
 }
 
 void DownloadFileImpl::SendUpdate() {
   BrowserThread::PostTask(
       BrowserThread::UI, FROM_HERE,
       base::Bind(&DownloadManager::UpdateDownload,
                  download_manager_, id_.local(),
                  BytesSoFar(), CurrentSpeed(), GetHashState()));
 }