byRows property
Define the max height of the dropdown using the number of dropdown rows, for example, if byRows = 3, the height of the dropdown will be equal to the height of three rows. The user will have to scroll if the list grows larger.
This is double because sometimes, you don't want, for example, 5 exact rows, but something more like 5.5 (only show half of the 6th rows) just to let the user know that the dropdown is scrollable -- that there is more stuff below.
This will be ignored if byPixels is provided
Implementation
final double byRows;