Distance( const nsReadingIterator<PRUnichar>&aStart, const nsReadingIterator<PRUnichar>&aEnd )
Distance( const nsReadingIterator<char>&aStart, const nsReadingIterator<char>&aEnd )
Distance( const nsReadingIterator<PRUnichar>&aStart, const nsReadingIterator<PRUnichar>&aEnd )  {    return Distance_Impl(aStart, aEnd);  }