getPadding() {
    return {
      left: this.paddingLeft || 0,
      top: this.paddingTop || 0,
      right: this.paddingRight || 0,
      bottom: this.paddingBottom || 0
    };
  }
Get the padding needed for the scale
@return {{top: number, left: number, bottom: number, right: number}} the necessary padding
@private