Add --xattr-set-filesize option (Fixes #1348)

youtube_dl/options.py

@@ -394,6 +394,10 @@ def parseOpts(overrideArguments=None):
         '--playlist-reverse',
         action='store_true',
         help='Download playlist videos in reverse order')
+    downloader.add_option(
+        '--xattr-set-filesize',
+        dest='xattr_set_filesize', action='store_true',
+        help='(experimental) set file xattribute ytdl.filesize with expected filesize')
     downloader.add_option(
         '--external-downloader',
         dest='external_downloader', metavar='COMMAND',