function parseExpression(noComma, noIn) {
    var expr = parseMaybeAssign(noIn);
    if (!noComma && tokType === _comma) {
      var node = startNodeFrom(expr);
      node.expressions = [expr];
      while (eat(_comma)) node.expressions.push(parseMaybeAssign(noIn));
      return finishNode(node, "SequenceExpression");
    }
    return expr;
  }
Parse a full expression. The arguments are used to forbid comma
sequences (in argument lists, array literals, or object literals)
or the `in` operator (in for loops initalization expressions).

@param {boolean=} noComma
@param {boolean=} noIn
@returns {!node_t}