_drawHintLabels(painter, stats) {
        let gridRect = this._rectForSuperpositionDisplay();

        // Amplitude hint.
        painter.print(
            'Final amplitudes',
            gridRect.right() + 3,
            gridRect.bottom() + 3,
            'left',
            'top',
            'gray',
            '12px sans-serif',
            100,
            20);

        // Deferred measurement warning.
        if (this.circuitDefinition.colIsMeasuredMask(Infinity) !== 0) {
            painter.printParagraph(
                "(assuming measurement deferred)",
                new Rect(
                    gridRect.right() + 3,
                    gridRect.bottom() + 20,
                    100,
                    75),
                new Point(0.5, 0),
                'red');
        }

        // Discard rate warning.
        let survivalRate = stats.survivalRate(Infinity);
        if (Math.abs(survivalRate - 1) > 0.01) {
            let desc;
            if (survivalRate < 1) {
                let rate = Math.round(survivalRate * 100);
                let rateDesc = survivalRate === 0 ? "0" :
                    rate > 0 ? rate :
                    "<1";
                desc = `kept: ${rateDesc}%`;
            } else {
                let factor = Math.round(survivalRate * 100);
                desc = `over-unity: ${factor}%`;
            }
            painter.print(
                desc,
                this._rectForSuperpositionDisplay().x - 5,
                gridRect.bottom() + SUPERPOSITION_GRID_LABEL_SPAN,
                'right',
                'bottom',
                'red',
                '14px sans-serif',
                800,
                50);
        }
    }
Draws a peek gate on each wire at the right-hand side of the circuit.

@param {!Painter} painter
@param {!CircuitStats} stats
@private