Scales and positions its child within itself.
The fit and alignment arguments must not be null.
Source
RenderFittedBox({
RenderBox child,
ImageFit fit: ImageFit.contain,
FractionalOffset alignment: FractionalOffset.center
}) : _fit = fit, _alignment = alignment, super(child) {
assert(fit != null);
assert(alignment != null && alignment.dx != null && alignment.dy != null);
}