turns a simple model spec with one process (browser process) and one
   * thread (CrBrowserMain).
   *
   * It does not contain any slices or expectations - those should be added
   * manually.
   *
   * This is a function instead of just a variable because the test functions
   * are meant to modify this modelSpec and insert suitable expectations.
   */
  function getSimpleModelSpec_() {
    return {
      processes: [
        {
          name: 'Browser',
          pid: 12345,
          threads: [
        