third_party/WebKit/LayoutTests/http/tests/serviceworker/resources/stop-worker-with-pending-fetch.js

self.addEventListener('fetch', evt => {
    // Retruns an empty response to resolve with_iframe() in the test page.
    evt.respondWith(new Response(''));
    // Keeps this event alive.
    evt.waitUntil(new Promise(function() {}));
  });