third_party/WebKit/LayoutTests/http/tests/serviceworker/resources/fetch-response-xhr-iframe.html

<script src="../../resources/testharness.js"></script>
<script src="test-helpers.js"></script>
<script>

function xhr_send(method, data) {
  return new Promise(function(resolve, reject) {
      var xhr = new XMLHttpRequest();
      xhr.onload = function() {
        resolve(xhr);
      };
      xhr.onerror = function() {
        reject('XHR should succeed.');
      };
      xhr.responseType = 'text';
      xhr.open(method, './dummy?test', true);
      xhr.send(data);
    });
}

function coalesce_headers_test() {
  return xhr_send('POST', 'test string')
  .then(function(xhr) {
      assert_equals(xhr.getResponseHeader('foo'), 'foo, bar');
    });
}

window.addEventListener('message', function(evt) {
    var port = evt.ports[0];
    coalesce_headers_test()
      .then(function() { port.postMessage({results: 'finish'}); })
      .catch(function(e) { port.postMessage({results: 'failure:' + e}); });
  });
</script>