chrome/test/data/extensions/api_test/fileapi/background.js

// Copyright 2011 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

var fileSystem = null;

console.log("Requesting a filesystem...");
webkitRequestFileSystem(window.TEMPORARY, 100, getFileSystem, errorCallback);

function getFileSystem(fs) {
  fileSystem = fs;
  console.log("DONE requesting filesystem: " + fileSystem.name);
  fileSystem.root.getDirectory('dir', {create:true},
                               directoryCallback, errorCallback);
}

function directoryCallback(directory) {
  console.log("DONE creating directory: " + directory.path);
  directory.getFile('file', {create:true}, fileCallback, errorCallback);
}

function fileCallback(file) {
  console.log("DONE creating file: " + file.path);

  // See if we get the same filesystem space in the tab.
  console.log("Opening tab...");
  chrome.tabs.create({
    url: "tab.html"
  });
}

function errorCallback(error) {
  chrome.test.fail("Got unexpected error: " + error.code);
}