code: function(
      dateTimePattern, fallbackPattern, dateTimeSymbols) {
    /**
     * Date time pattern used to format the dates.
     * @private {string}
     */
    this.dateTimePattern_ = dateTimePattern;
  
    /**
     * Date time formatter used to format the dates.
     * @private {!DateTimeFormat}
     */
    this.dateTimeFormatter_ =
        new DateTimeFormat(dateTimePattern, dateTimeSymbols);
  
    /**
     * Fallback interval pattern.
     * @private {string}
     */
    this.fallbackPattern_ = fallbackPattern;
  }
docs: Constructs a DateTimeFormatter_ object which implements the Formatter_
  interface.
  
  Internal object to construct and store a goog.i18n.DateTimeFormat for the
  a datetime pattern and formats dates using the fallback interval pattern
  (e.g. '{0} – {1}').
  
  @param {string} dateTimePattern Datetime pattern used to format the dates.
  @param {string} fallbackPattern Fallback interval pattern to be used with the
  datetime pattern.
  @param {!DateTimeSymbolsType} dateTimeSymbols Symbols to use with
  the datetime format.
  @constructor
  @implements {Formatter_}
  @private