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

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

Index: chrome/browser/chromeos/login/users/fake_chrome_user_manager.cc
diff --git a/chrome/browser/chromeos/login/users/fake_chrome_user_manager.cc b/chrome/browser/chromeos/login/users/fake_chrome_user_manager.cc
index 299058ba1812ff09fa0f0b401ce70bd6a5a3d5d9..3cf877b8fa36d7575eb36989323dd2299a118fea 100644
--- a/chrome/browser/chromeos/login/users/fake_chrome_user_manager.cc
+++ b/chrome/browser/chromeos/login/users/fake_chrome_user_manager.cc
@@ -111,25 +111,25 @@ void FakeChromeUserManager::ResetUserFlow(const std::string& email) {
   }
 }
 
-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) {
 }