getIcuFormattingPatternsForUnit_(unit) {
    assert(
        this.checkIfLegalUnit_(unit),
        'Unit must be years, months, weeks, days, hours, minutes or seconds');
    switch (unit) {
      default:
      case DurationFormatUnit.YEAR:
        return this.durationSymbols_.YEAR;
      case DurationFormatUnit.MONTH:
        return this.durationSymbols_.MONTH;
      case DurationFormatUnit.WEEK:
        return this.durationSymbols_.WEEK;
      case DurationFormatUnit.DAY:
        return this.durationSymbols_.DAY;
      case DurationFormatUnit.HOUR:
        return this.durationSymbols_.HOUR;
      case DurationFormatUnit.MINUTE:
        return this.durationSymbols_.MINUTE;
      case DurationFormatUnit.SECOND:
        return this.durationSymbols_.SECOND;
    }
  }
Use public unit symbol to retrieve data for that unit.
@param {string} unit
@return {!DurationSymbolsFormatStyles}
@private