getIcuFormattingPatternForStyle_(unitInfo) {
    // Fall back from LONG to NARROW to SHORT as needed.
    switch (this.style_) {
      case DurationFormatStyle.LONG:
        if (unitInfo.LONG != undefined) {
          return unitInfo.LONG;
        }
      case DurationFormatStyle.NARROW:
        if (unitInfo.NARROW != undefined) {
          return unitInfo.NARROW;
        }
      case DurationFormatStyle.SHORT:
      default:
        return unitInfo.SHORT;
    }
  }
Use unit symbol to retrieve data for that unit, given the style.
@param{!DurationSymbolsFormatStyles} unitInfo
@return {string}
@private