void cubicTo(double x1, double y1, double x2, double y2, double x3, double y3)

Adds a cubic bezier segment that curves from the current point to the given point (x3,y3), using the control points (x1,y1) and (x2,y2).

Source 

void cubicTo(double x1, double y1, double x2, double y2, double x3, double y3) native "Path_cubicTo";