function CrossFilter(params) {
    Transform.call(this, Bitmaps(), params);
    this._indices = null;
    this._dims = null;
  }
An indexed multi-dimensional filter.
@constructor
@param {object} params - The parameters for this operator.
@param {Array<function(object): *>} params.fields - An array of dimension accessors to filter.
@param {Array} params.query - An array of per-dimension range queries.