code: function(ids, options) {
              options = options || {};
              options.idsToFetch = _.intersection(ids, this.getTrackedIds());
              return this.fetch(options);
            }
docs: Will force the cache to fetch a subset of this collection's tracked ids
  @method requesterMixin.fetchByIds
  @param ids {Array} array of model ids
  @param [options] {Object} if given, will pass the options argument to this.fetch. Note, will not affect options.idsToFetch
  @return {Promise} promise that will resolve when the fetch is complete