controller property Null safety
Whether a rasterized version of this render objects child is drawn in place of the child.
Implementation
RasterWidgetController get controller => _controller;
Implementation
set controller(RasterWidgetController value) {
  if (value == controller) {
    return;
  }
  controller.removeListener(_onRasterValueChanged);
  final bool oldValue = controller.rasterize;
  _controller = value;
  if (attached) {
    controller.addListener(_onRasterValueChanged);
    if (oldValue != controller.rasterize) {
      _onRasterValueChanged();
    }
  }
}