onPaint method
Draws segment in series bounds.
Implementation
@override
void onPaint(Canvas canvas) {
  _computeAreaPath();
  Paint paint = getFillPaint();
  if (paint.color != Colors.transparent) {
    canvas.drawPath(_fillPath, paint);
  }
  paint = getStrokePaint();
  if (paint.color != Colors.transparent && paint.strokeWidth > 0) {
    drawDashes(canvas, series.dashArray, paint, path: _strokePath);
  }
}