cpuTimeDensity = event.cpuSelfTime / event.selfTime;
    return getWallClockSelfTime_(event, rangeOfInterest) * cpuTimeDensity;
  }

  /**
  * @callback getEventAttributeCallback
  * @param {!tr.b.Event} event The event to read an attribute from.
  * @return {number} The value of the attribute.
  */

  /**
  * Generate a breakdown tree from all slices of |mainThread| in
  * |rangeOfInterest|. The callback function |getEventSelfTime| specify how to
  * get self time from a given event.
  *
  * @param  {!tr.m