ither
   *
   *   1. The beginning of the next navigationStart event or
   *   2. The end of the trace
   *
   * This function only works when timestamps are from the same renderer. If
   * windows for multiple renderers need to be computed, the timestamps should
   * be separated for each renderer and this function should be called
   * separately for each.
   *
   * @param {!Array.<number>} interactiveTimestamps
   * @param {!Array.<number>} navStartTimestamps
   * @param {!number} traceEndTimestamp
   * 