parseExpression_(allowIn) {
    let coverInitializedNameCount = this.coverInitializedNameCount_;
    let expression = this.parseExpressionAllowPattern_(allowIn);
    this.ensureNoCoverInitializedNames_(expression, coverInitializedNameCount);
    return expression;
  }
Expression :
  AssignmentExpression
  Expression , AssignmentExpression

ExpressionNoIn :
  AssignmentExpressionNoIn
  ExpressionNoIn , AssignmentExpressionNoIn

@return {ParseTree}