_paintGatesInGroup(painter, hand, groupIndex) {
        let group = this.toolboxGroups[groupIndex];
        let r = this.groupLabelRect(groupIndex);
        painter.print(
            group.hint,
            r.x + r.w/2,
            r.y + r.h/2,
            'center',
            'middle',
            'black',
            '16px sans-serif',
            r.w,
            r.h);

        for (let gateIndex = 0; gateIndex < group.gates.length; gateIndex++) {
            let gate = group.gates[gateIndex];
            if (gate === undefined) {
                continue;
            }
            let rect = this.gateDrawRect(groupIndex, gateIndex);
            DisplayedToolbox._paintGate(painter, hand, gate, rect, false, CircuitStats.EMPTY);
        }
    }
@param {!Painter} painter
@param {!Hand} hand
@param {!int} groupIndex
@private