nsresult rv;  nsCOMPtr<nsIPrefBranch> prefBranch = do_QueryInterface(mPrefService, &rv); if (NS_SUCCEEDED(rv)) rv = prefBranch->DeleteBranch(aStartingAt); return rv;
return _convertRes(PREF_DeleteBranch(branchName));
NS_IMETHODIMP nsPref::DeleteBranch(const char *aStartingAt){  nsresult rv;  nsCOMPtr<nsIPrefBranch> prefBranch = do_QueryInterface(mPrefService, &rv);  if (NS_SUCCEEDED(rv))    rv = prefBranch->DeleteBranch(aStartingAt);  return rv;}