 slightly extend past the start time of the next.
        if (durationBetweenTasks < -1e7) {
          throw new Error('Internal Error: List of tasks used to construct ' +
                          'TaskCluster must be sorted.');
        }
      }

      this._clusterTasks = tasksInClusterSorted;
    }

    /**
     * @type{number}
     */
    get start() {
      return this._clusterTasks[0].start;
    }

    /**
     * @type{number}
     */
    get end() {
      return this._clusterTasks[this._clusterTasks