*aDestLength = 2*aSrcLength;
if(0 != mBOM) *aDestLength = 2*(aSrcLength+1); else *aDestLength = 2*aSrcLength;
NS_IMETHODIMP nsUnicodeToUCS2BE::GetMaxLength(const PRUnichar * aSrc,                                               PRInt32 aSrcLength,                                              PRInt32 * aDestLength){  *aDestLength = 2*aSrcLength;  return NS_OK_UENC_EXACTLENGTH;}