<!DOCTYPE html>
<html>
<head>
<style>
#flex-box-in-main-frame {
    display: -webkit-box;
    -webkit-box-orient: vertical;
}
</style>
<script>
if (window.testRunner) {
    testRunner.dumpAsText();
    testRunner.waitUntilDone();
}

if (window.internals)
    internals.settings.setFrameFlattening("FullyEnabled")

function runTest()
{
    var iframeDocument = document.getElementById("iframe").contentDocument;
    iframeDocument.getElementById("container").style.display = "inline"; // Removes anonymous wrapper around "This is some inline text."
    iframeDocument.body.offsetWidth; // Force layout

    document.getElementById("console").innerText = "PASS";

    if (window.testRunner)
        testRunner.notifyDone();
}
</script>
</head>
<body>
<p>Test that the layout of a frame-flattened &lt;iframe&gt; inside a flex box doesn't try to modify the list of elements in the main frame that are waiting for a scroll update. This test passed if you see the word PASS below. Otherwise, it failed.</p>
<div id="flex-box-in-main-frame">
    <!-- Note, we defer scroll updates to this flex box until we finish the layout of its children. -->
    <iframe id="iframe" onload="runTest()" width="20%" height="20%" scrolling="auto" srcdoc="
        <div id='container'>
            This is some inline text.
            <p>This is some text in a block.</p>
        </div>
    "></iframe>
</div>
<pre id="console">FAIL</pre>
</body>
</html>