LayoutTests/loader/load-defer.html

<!DOCTYPE html>
<html>
<script>
if (window.testRunner) {
    testRunner.dumpAsText();
    testRunner.waitUntilDone();
}

var testFrame;

function loadedTooEarly()
{
    alert("FAIL: The frame loaded while loads were deferred.");
    testRunner.notifyDone();
}

function passAndFinish()
{
    alert("PASS: The frame loaded after loads were resumed.");
    testRunner.notifyDone();
}

function resumeLoads()
{
    testFrame.onload = passAndFinish;
    if (window.testRunner)
        testRunner.setDefersLoading(false);
}

function runTest()
{
    alert("Test that load deferring works as intended.");
    if (window.testRunner)
        testRunner.setDefersLoading(true);

    testFrame = document.createElement("iframe");
    testFrame.onload = loadedTooEarly;
    testFrame.src = "resources/images.html";
    document.body.appendChild(testFrame);
    setTimeout(resumeLoads, 100);
}

</script>
<body onload='runTest()'>
</body>
</html>