To draw a line with a rounded end in skia you need to change the StrokeCap to Round. Here is a simple example using Delphi:

procedure drawRoundedLine (ACanvas : ISkCanvas; x1, y1, x2, y2 : single);
var LPaint : ISkPaint;
begin 
  LPaint := TSkPaint.Create;
  LPaint.AntiAlias := True;
  LPaint.Color := TAlphaColors.Blue;
  LPaint.StrokeWidth := 2;
  LPaint.Style := TSkPaintStyle.Stroke;
  LPaint.StrokeCap := TSkStrokeCap.Round; 

  ACanvas.DrawLine(x1, y1, x2, y2, LPaint);
end;