We should use UserID object to identify users instead of username.

chrome/browser/chromeos/login/users/fake_chrome_user_manager.cc

 // 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.
 
 #include "chrome/browser/chromeos/login/users/fake_chrome_user_manager.h"
 
 #include "chrome/browser/chromeos/login/users/chrome_user_manager.h"
 #include "chrome/browser/chromeos/login/users/fake_supervised_user_manager.h"
 #include "chrome/browser/chromeos/profiles/profile_helper.h"
 #include "chrome/browser/chromeos/settings/cros_settings.h"
@@ skipping 93 matching lines @@
 }
 
 void FakeChromeUserManager::ResetUserFlow(const std::string& email) {
   FlowMap::iterator it = specific_flows_.find(email);
   if (it != specific_flows_.end()) {
     delete it->second;
     specific_flows_.erase(it);
   }
 }
 
-void FakeChromeUserManager::SwitchActiveUser(const std::string& email) {
-  active_user_id_ = email;
+void FakeChromeUserManager::SwitchActiveUser(const UserID& user_id /*email*/) {

[Denis Kuznetsov (DE-MUC), 2015/06/10 16:50:45]

drop commented part

+  active_user_id_ = user_id;
   ProfileHelper::Get()->ActiveUserHashChanged(
-      ProfileHelper::GetUserIdHashByUserIdForTesting(email));
+      ProfileHelper::GetUserIdHashByUserIdForTesting(user_id.GetUserEmail()));
   if (!users_.empty() && !active_user_id_.empty()) {
     for (user_manager::User* user : users_)
-      user->set_is_active(user->email() == active_user_id_);
+      user->set_is_active(user->user_id() == active_user_id_);
   }
 }
 
-const std::string& FakeChromeUserManager::GetOwnerEmail() const {
-  return owner_email_;
+const user_manager::UserID& FakeChromeUserManager::GetOwnerID() const {
+  return owner_id_;
 }
 
 void FakeChromeUserManager::SessionStarted() {
 }
 
 void FakeChromeUserManager::RemoveUser(
-    const std::string& email,
+    const UserID& user_id,
     user_manager::RemoveUserDelegate* delegate) {
 }
 
 user_manager::UserList
 FakeChromeUserManager::GetUsersAllowedForSupervisedUsersCreation() const {
   CrosSettings* cros_settings = CrosSettings::Get();
   bool allow_new_user = true;
   cros_settings->GetBoolean(kAccountsPrefAllowNewUser, &allow_new_user);
   bool supervised_users_allowed = AreSupervisedUsersAllowed();
 
@@ skipping 36 matching lines @@
   return false;
 }
 
 void FakeChromeUserManager::UpdateKnownUserPrefs(
     const user_manager::UserID& user_id,
     const base::DictionaryValue& values,
     bool clear) {
 }
 
 }  // namespace chromeos