InkFeature constructor

InkFeature({@required MaterialInkController controller, @required RenderBox referenceBox, VoidCallback onRemoved })

Initializes fields for subclasses.

Implementation 

InkFeature({
  @required MaterialInkController controller,
  @required this.referenceBox,
  this.onRemoved,
}) : assert(controller != null),
     assert(referenceBox != null),
     _controller = controller;