third_party/WebKit/LayoutTests/http/tests/serviceworker/resources/fetch-request-with-gc-iframe.html - chromium/src - Git at Google

 <!doctype html>
 <script>
 window.addEventListener('message', event => {
     const port = event.ports[0];
     fetch('empty', {method: 'POST', body: 'hello'})
       .then(() => port.postMessage({results: 'finish'}))
       .catch(e => port.postMessage({results: 'failure:' + e}));
   });
 </script>
	<!doctype html>
	<script>
	window.addEventListener('message', event => {
	const port = event.ports[0];
	fetch('empty', {method: 'POST', body: 'hello'})
	.then(() => port.postMessage({results: 'finish'}))
	.catch(e => port.postMessage({results: 'failure:' + e}));
	});
	</script>