function parseMaybeConditional(noIn) {
    var expr = parseExprOps(noIn);
    if (eat(_question)) {
      var node = startNodeFrom(expr);
      node.test = expr;
      node.consequent = parseExpression(true);
      expect(_colon);
      node.alternate = parseExpression(true, noIn);
      return finishNode(node, "ConditionalExpression");
    }
    return expr;
  }
Parse a ternary conditional (`?:`) operator.

@param {boolean|undefined} noIn
@returns {!node_t}