From the current point in the path, draw a bezier curve to endX and endY
Source
GraphicsCommandBezierCurveTo bezierCurveTo(num controlX1, num controlY1, num controlX2, num controlY2, num endX, num endY) {
var command = new GraphicsCommandBezierCurveTo(controlX1, controlY1, controlX2, controlY2, endX, endY);
this.addCommand(command);
return command;
}