nsCOMPtr<nsIPrincipal> principal; GetDocumentPrincipal(getter_AddRefs(principal));
GetDocumentPrincipal();
nsXULPrototypeDocument::SetURI(nsIURI* aURI){    NS_ASSERTION(!mURI, "Can't change the uri of a xul prototype document");    if (mURI)        return NS_ERROR_ALREADY_INITIALIZED;    mURI = aURI;    if (!mDocumentPrincipal) {        // If the document doesn't have a principal yet we'll force the creation of one        // so that mNodeInfoManager properly gets one.        nsCOMPtr<nsIPrincipal> principal;        GetDocumentPrincipal(getter_AddRefs(principal));    }    return NS_OK;}