rate of the
  // BattOr.
  const CHROME_POWER_GRACE_PERIOD_MS = 1;

  /**
   * Creates an empty histogram to hold data for a given time interval.
   *
   * @returns {Object} An object of the form:
   *
   *   {
   *     perSecond {boolean}: Whether the data for this time interval is given
   *       as per second, If not, it's given as an integral over the
   *       whole interval.
   *     energy {tr.v.Histogram}: Histogram giving energy use (i.e. energy in J
   *       if perSecond = False, power in W if