Add User Testing interface to impl/memory.

impl/prod/user.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 prod
 
 import (
         gae_user "github.com/luci/gae/service/user"
         "golang.org/x/net/context"
         "google.golang.org/appengine/user"
@@ skipping 35 matching lines @@
         usr, err := user.CurrentOAuth(u.aeCtx, scopes...)
         if err != nil {
                 return nil, err
         }
         return (*gae_user.User)(usr), nil
 }
 
 func (u userImpl) OAuthConsumerKey() (string, error) {
         return user.OAuthConsumerKey(u.aeCtx)
 }
+
+func (u userImpl) Testable() gae_user.Testable {
+        return nil
+}