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

impl/dummy/dummy.go

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 package dummy
 
 import (
         "fmt"
         "runtime"
         "strings"
@@ skipping 133 matching lines @@
 func (i) GetNamespace() string                                                     { return "dummy-namespace" }
 func (i) ModuleHostname(module, version, instance string) (string, error)          { panic(ni()) }
 func (i) ModuleName() string                                                       { panic(ni()) }
 func (i) DefaultVersionHostname() string                                           { panic(ni()) }
 func (i) PublicCertificates() ([]info.Certificate, error)                          { panic(ni()) }
 func (i) RequestID() string                                                        { panic(ni()) }
 func (i) ServiceAccount() (string, error)                                          { panic(ni()) }
 func (i) SignBytes(bytes []byte) (keyName string, signature []byte, err error)     { panic(ni()) }
 func (i) VersionID() string                                                        { panic(ni()) }
 func (i) Namespace(namespace string) (context.Context, error)                      { panic(ni()) }
+func (i) MustNamespace(namespace string) context.Context                           { panic(ni()) }
 func (i) Datacenter() string                                                       { panic(ni()) }
 func (i) InstanceID() string                                                       { panic(ni()) }
 func (i) IsDevAppServer() bool                                                     { panic(ni()) }
 func (i) ServerSoftware() string                                                   { panic(ni()) }
 func (i) IsCapabilityDisabled(err error) bool                                      { panic(ni()) }
 func (i) IsOverQuota(err error) bool                                               { panic(ni()) }
 func (i) IsTimeoutError(err error) bool                                            { panic(ni()) }
 
 var dummyInfoInst = i{}
 
@@ skipping 29 matching lines @@
 func (m) Send(*mail.Message) error         { panic(ni()) }
 func (m) SendToAdmins(*mail.Message) error { panic(ni()) }
 func (m) Testable() mail.Testable          { panic(ni()) }
 
 var dummyMailInst = m{}
 
 // Mail returns a dummy mail.Interface implementation suitable for embedding.
 // Every method panics with a message containing the name of the method which
 // was unimplemented.
 func Mail() mail.Interface { return dummyMailInst }