chromium/content/test/data/service_worker/fetch_event_blob.js

// Copyright 2015 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

this.onfetch = function(event) {
    var blob = new Blob(['<title>Title</title>']);
    var response = new Response(blob, {
        headers: { 'Content-Type': 'text/html' }
    });
    event.respondWith(response);
};