xAxisPadding (padding) {
        if (!arguments.length) {
            return this._xAxisPadding;
        }
        this._xAxisPadding = padding;
        return this;
    }
Set or get x axis padding for the elastic x axis. The padding will be added to both end of the x
axis if elasticX is turned on; otherwise it is ignored.

Padding can be an integer or percentage in string (e.g. '10%'). Padding can be applied to
number or date x axes.  When padding a date axis, an integer represents number of units being padded
and a percentage string will be treated the same as an integer. The unit will be determined by the
xAxisPaddingUnit variable.
@param {Number|String} [padding=0]
@returns {Number|String|CoordinateGridMixin}