chromium/src/third_party/blink/web_tests/http/tests/background_sync/chromium/resources/stop-worker-no-crash-worker.js

self.addEventListener('sync', event => {
  // Keeps this event alive.
  event.waitUntil(new Promise(function () { }));
});

self.addEventListener('periodicsync', event => {
  // Keeps this event alive.
  event.waitUntil(new Promise(function () { }));
});

// We need this fetch handler to check the sanity of the SW using iframe().
self.addEventListener('fetch', event => {
  event.respondWith(new Response(''));
});