NS_ADDREF(aDataSource);
CompositeDataSourceImpl::AddDataSource(nsIRDFDataSource* aDataSource){    NS_ASSERTION(aDataSource != nsnull, "null ptr");    if (! aDataSource)        return NS_ERROR_NULL_POINTER;    mDataSources.AppendElement(aDataSource);    aDataSource->AddObserver(this);    NS_ADDREF(aDataSource);    return NS_OK;}