scaledOutwardBy(factor) {
        let c = this.center();
        let w2 = this.w * factor;
        let h2 = this.h * factor;
        return new Rect(c.x - w2/2, c.y - h2/2, w2, h2);
    }
Returns the result of scaling the rectangle w.r.t. its center by the given scaling factor.
@param {!number} factor
@returns {!Rect}