clients-get-client-types-frame.html

<!DOCTYPE html>
<script>
fetch('clientId')
  .then(function(response) {
      return response.text();
    })
  .then(function(text) {
      parent.postMessage({clientId: text}, '*');
    });

onmessage = function(e) {
  if (e.data == 'StartWorker') {
    var w = new Worker('clients-get-client-types-frame-worker.js');
    w.postMessage({cmd:'GetClientId', port:e.ports[0]}, [e.ports[0]]);
  }
}
</script>

chromium/third_party/blink/web_tests/external/wpt/service-workers/service-worker/resources/clients-get-client-types-frame.html