function GroupTotals() {
    this.__groupTotals = true;

    /***
     * Parent Group.
     * @param group
     * @type {Group}
     */
    this.group = null;

    /***
     * Whether the totals have been fully initialized / calculated.
     * Will be set to false for lazy-calculated group totals.
     * @param initialized
     * @type {Boolean}
     */
    this.initialized = false;
  }
Information about group totals.
An instance of GroupTotals will be created for each totals row and passed to the aggregators
so that they can store arbitrary data in it.  That data can later be accessed by group totals
formatters during the display.
@class GroupTotals
@extends Slick.NonDataItem
@constructor