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chromium/third_party/blink/web_tests/external/wpt/focus/support/activeelement-after-immediately-focusing-same-site-iframe-outer.html 

<!doctype html>
<meta charset="utf-8">
<title>activeElement when focusing same-site iframe</title>
<script>
let log = "";
function getLog() {
    return log;
}
window.onmessage = function(e) {
    log += e.data;
};
</script>
<iframe src="activeelement-after-immediately-focusing-same-site-iframe-inner.html"></iframe>
<script>
log += "outerparse,";
log += "activeElement:" + document.activeElement.tagName + ",";
log += "willfocusiframe,";
document.getElementsByTagName("iframe")[0].focus();
log += "didfocusiframe,";
log += "activeElement:" + document.activeElement.tagName + ",";
log += "willbluriframe,";
document.getElementsByTagName("iframe")[0].blur();
log += "didbluriframe,";
log += "activeElement:" + document.activeElement.tagName + ",";
log += "willspineventloop,"
opener.step_timeout(function() {
    opener.postMessage(getLog(), "*");
}, 1500);
</script>