LayoutTests/http/tests/misc/resources/prefetch-purpose.php

<?php setcookie("Purpose", $_SERVER["HTTP_PURPOSE"]);

if (isset($_COOKIE['Purpose'])) {
    setcookie("Purpose", "", time() - 3600);
    echo "<h1>The cookie was set!</h1>";
    echo "<p>Purpose: ";
    echo $_COOKIE['Purpose'];
} else {
    echo "<h1>BAD BROWSER NO COOKIE</h1>";
}
?>

<script>
testRunner.notifyDone();
</script>

<p>This test verifies that prefetches are sent with the HTTP request header
<b>Purpose: prefetch</b>.  To do this, the root page has a prefetch
link targetting this subresource which contains a PHP script
(resources/prefetch-purpose.php).  That initial prefetch of this
resource sets a cookie.  Later, the root page sets window.location to
target this script, which verifies the presence of the cookie, and
generates the happy test output that you hopefully see right now.