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chromium/third_party/blink/web_tests/external/wpt/focus/support/focus-already-focused-iframe-different-site-outer.sub.html 

<!doctype html>
<meta charset="utf-8">
<title>Focus already focused iframe</title>
<script>
let failed = false;
window.onmessage = function(e) {
    if (e.data == "focus") {
        document.getElementsByTagName("iframe")[0].focus();
        opener.step_timeout(function() {
            if (failed) {
                opener.postMessage("FAIL", "*");
            } else {
                opener.postMessage("PASS", "*");
            }
        }, 1500);
    } else if (e.data == "FAIL") {
        failed = true;
    }
}
</script>
<iframe src="http://{{hosts[alt][www]}}:{{ports[http][0]}}/focus/support/focus-already-focused-iframe-inner.html"></iframe>