brushOn (brushOn) {
        if (!arguments.length) {
            return this._brushOn;
        }
        this._brushOn = brushOn;
        return this;
    }
Turn on/off the brush-based range filter. When brushing is on then user can drag the mouse
across a chart with a quantitative scale to perform range filtering based on the extent of the
brush, or click on the bars of an ordinal bar chart or slices of a pie chart to filter and
un-filter them. However turning on the brush filter will disable other interactive elements on
the chart such as highlighting, tool tips, and reference lines. Zooming will still be possible
if enabled, but only via scrolling (panning will be disabled.)
@param {Boolean} [brushOn=true]
@returns {Boolean|CoordinateGridMixin}