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

content/browser/download/download_file_impl.h

Index: content/browser/download/download_file_impl.h
diff --git a/content/browser/download/download_file_impl.h b/content/browser/download/download_file_impl.h
index b3630e5555a68077f67c0d67c62c161156d4b2a5..0392d9907365e5abdcc48fac6d8151cd94ee35f9 100644
--- a/content/browser/download/download_file_impl.h
+++ b/content/browser/download/download_file_impl.h
@@ -84,6 +84,9 @@ class CONTENT_EXPORT DownloadFileImpl : virtual public content::DownloadFile {
   // the DownloadFileManager for its internal record keeping.
   content::DownloadId id_;
 
+  // The default directory for creating the download file.
+  FilePath default_download_directory_;
+
   // Used to trigger progress updates.
   scoped_ptr<base::RepeatingTimer<DownloadFileImpl> > update_timer_;