code: function(direction) {
                  var currentOrder = this.state.order,
                      newOrder = currentOrder;
                  if (direction === PagingCollection.SortDirection.ASCENDING) {
                      newOrder = -1;
                  } else if (direction === PagingCollection.SortDirection.DESCENDING) {
                      newOrder = 1;
                  }
                  if (newOrder !== currentOrder) {
                      this.setSorting(this.state.sortKey, newOrder);
                      this.isStale = true;
                  }
              }
docs: Sets the direction of the sort and marks the collection
  as stale.  Assumes (and requires) that the sort key has
  already been set.
  
  @param direction {string} either ASCENDING or DESCENDING from
  PagingCollection.SortDirection.