ble to distinguish between these two
   * types of cpu idle time during the range |rangeOfInterest| not used by
   * events of the main thread |mainThreadEvents|.
   *
   * @param {!Object.<string, Object>} breakdownTree The breakdownTree that has
   * been generated by |generateTimeBreakdownTree|.
   * @param {!tr.b.Event} mainThreadEvents The top level events of the main
   * thread.
   * @param {!tr.b.Event} networkEvents The network events in the renderer.
   * @param {!tr.b.math.Range} rangeOfInterest 