chromium/third_party/blink/web_tests/external/wpt/html/dom/resources/self-origin-subframe.html

<script>
  window.onmessage = function(e){
    if (e.data == "getOrigin") {
      parent.postMessage(self.origin, "*");
    } else if (e.data == "setDomainAndGetOrigin") {
      var oldDomain = document.domain;
      try {
        document.domain = document.domain.replace(/^[^.]*./, "");
      } catch (e) {
        parent.postMessage("THREW WHEN SETTING DOMAIN: " + e, "*");
        return;
      }
      if (oldDomain === document.domain) {
        parent.postMessage("FAILED TO SET DOMAIN", "*");
      } else {
        parent.postMessage(self.origin, "*");
      }
    } else {
      parent.postMessage("UNEXPECTED MESSAGE", "*");
    }
  }
</script>