The maximum extent of tiles in the cross axis.
This delegate will select a cross-axis extent for the tiles that is as large as possible subject to the following conditions:
- The extent evenly divides the cross-axis extent of the grid.
- The extent is at most maxCrossAxisExtent.
For example, if the grid is vertical, the grid is 500.0 pixels wide, and maxCrossAxisExtent is 150.0, this delegate will create a grid with 4 columns that are 125.0 pixels wide.
final double maxCrossAxisExtent;