servo/tests/wpt/web-platform-tests/web-locks/resources/service-worker.js

// Responds to '/clientId' with the request's clientId.
self.addEventListener('fetch', e => {
  if (new URL(e.request.url).pathname === '/clientId') {
    e.respondWith(new Response(JSON.stringify({clientId: e.clientId})));
    return;
  }
});