* `{@link #numFromEdge}` rows of the grid viewport, if the required rows are available in the Store,// New start index should be current start index unless that's now too close to the end of the store// We only have to bump the table down by the height of removed rows if rows are not a standard size// We only have to bump the table down by the height of removed rows if rows are not a standard size// We only have to bump the table up by the height of top-added rows if rows are not a standard size// variableRowHeight is just a flag for the buffered rendering to know how to measure row height and