getRowBox method
Returns the position and dimensions of the box that the given row covers, in this render object's coordinate space (so the left coordinate is always 0.0).
The row being queried must exist.
This is only valid after layout.
Implementation
Rect getRowBox(int row) {
assert(row >= 0);
assert(row < rows);
assert(!debugNeedsLayout);
return Rect.fromLTRB(0.0, _rowTops[row], size.width, _rowTops[row + 1]);
}