The $GLOBALS array is directly manipulated and there is a variable $CHAT_HTMLHEAD_JS that is access via 'global' but which doesn't seem to be set anywhere.

Some like

"$GLOBALS['CFG']->wwwroot"

look like they could be replaced by

$CFG->wwwroot

.

Some like the following... I have no idea.

if ($info['quirks'] & QUIRK_CHUNK_UPDATE) {

    $output->html .= $GLOBALS['CHAT_DUMMY_DATA'];

    $output->html .= $GLOBALS['CHAT_DUMMY_DATA'];

    $output->html .= $GLOBALS['CHAT_DUMMY_DATA'];

}