Add a MustNamespace that panics if the namespace wasn't valid

impl/prod/info.go

Index: impl/prod/info.go
diff --git a/impl/prod/info.go b/impl/prod/info.go
index f1235585e3e26ae11c52c4d75007ca22d855224c..a4a67a87be21f02c0e3d9e0ec0e8d955b6edb04f 100644
--- a/impl/prod/info.go
+++ b/impl/prod/info.go
@@ -77,6 +77,13 @@ func (g giImpl) Namespace(namespace string) (context.Context, error) {
 	pc.namespace = namespace
 	return withProbeCache(usrCtx, &pc), nil
 }
+func (g giImpl) MustNamespace(ns string) context.Context {
+	ret, err := g.Namespace(ns)
+	if err != nil {
+		panic(err)
+	}
+	return ret
+}
 func (g giImpl) PublicCertificates() ([]info.Certificate, error) {
 	certs, err := appengine.PublicCertificates(g.aeCtx)
 	if err != nil {