Adds a row to the end of the table.
The newly added children must not already have parents.
Source
void addRow(List<RenderBox> cells) {
assert(cells.length == columns);
assert(_children.length == rows * columns);
_rows += 1;
_children.addAll(cells);
for (RenderBox cell in cells) {
if (cell != null)
adoptChild(cell);
}
markNeedsLayout();
}