constructor(identifierGenerator, reporter, options) {
    super(identifierGenerator, reporter, options);
    this.inDerivedClass_ = false;
    this.inConstructor_ = false;
  }
Desugars arrow function expressions

@see <a href="http://wiki.ecmascript.org/doku.php?id=strawman:arrow_function_syntax">strawman:arrow_function_syntax</a>