LayoutTests/http/tests/security/sync-xhr-partition.html

<script>
if (window.testRunner) {
    testRunner.dumpAsText();
    testRunner.waitUntilDone();
    internals.settings.setStorageBlockingPolicy('BlockThirdParty');
}
var async = new XMLHttpRequest();
async.onreadystatechange = function () {
    if (async.readyState === 4) {
        alert("Verifying credentials are used when given: " + async.responseText);
        var sync = new XMLHttpRequest();
        sync.open("GET", 'resources/basic-auth.py', false);
        sync.send();
        alert("Verifying credentials are used preemptively for sync xhr: " + sync.responseText);
        if (window.testRunner)
            testRunner.notifyDone();
    }
};
async.open('GET', 'resources/basic-auth.py', true, "username", "password");
async.send();
</script>