Gradient constructor

const Gradient({@required List<Color> colors, List<double> stops })

Initialize the gradient's colors and stops.

The colors argument must not be null, and must have at least two colors (the length is not verified until the createShader method is called).

If specified, the stops argument must have the same number of entries as colors (this is also not verified until the createShader method is called).

Implementation 

const Gradient({
  @required this.colors,
  this.stops,
}) : assert(colors != null);