_findModificationIndex_helperColRow(hand) {
        if (hand.pos === undefined || hand.heldGate === undefined) {
            return undefined;
        }
        let pos = hand.pos.minus(hand.holdOffset).plus(new Point(Config.GATE_RADIUS, Config.GATE_RADIUS));
        let halfColIndex = this.findOpHalfColumnAt(pos);
        let row = this.indexOfDisplayedRowAt(pos.y);
        if (halfColIndex === undefined || row === undefined) {
            return undefined;
        }
        let col = Math.ceil(halfColIndex);
        return {col, row, halfColIndex};
    }
@param {!Hand} hand
@returns {undefined|!{col: !int, row: !int, halfColIndex: !number}}
@private