chromium/third_party/blink/web_tests/http/tests/xmlhttprequest/resources/multipart-post-echo-filenames.php

<?php
header('Access-Control-Allow-Origin: *');
$first = True;
foreach ($_FILES as $file) {
    if (!$first)
        echo ",";
    echo $file['name'];
    $first = False;
}
?>