NS_INIT_ISUPPORTS();
PrefObserver::PrefObserver() :    mHostingFlags(kDefaultHostingFlags){    NS_INIT_ISUPPORTS();    nsresult rv = NS_OK;    mPrefService = do_GetService(NS_PREFSERVICE_CONTRACTID, &rv);    NS_ASSERTION(mPrefService, "where is the pref service?");}