From the current point in the path, draw a quadratic curve to endX and endY
Source
GraphicsCommandQuadraticCurveTo quadraticCurveTo(num controlX, num controlY, num endX, num endY) {
var command = new GraphicsCommandQuadraticCurveTo(controlX, controlY, endX, endY);
this.addCommand(command);
return command;
}