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

chrome/browser/chromeos/login/supervised/supervised_user_creation_controller_new.cc

Index: chrome/browser/chromeos/login/supervised/supervised_user_creation_controller_new.cc
diff --git a/chrome/browser/chromeos/login/supervised/supervised_user_creation_controller_new.cc b/chrome/browser/chromeos/login/supervised/supervised_user_creation_controller_new.cc
index 0e512ffe746c3d4930f4053f505ca29f7f011f66..8596ebe645abf17593c723c5caf4c2c25b7a4531 100644
--- a/chrome/browser/chromeos/login/supervised/supervised_user_creation_controller_new.cc
+++ b/chrome/browser/chromeos/login/supervised/supervised_user_creation_controller_new.cc
@@ -28,6 +28,7 @@
 #include "chromeos/login/auth/key.h"
 #include "chromeos/login/auth/user_context.h"
 #include "components/user_manager/user.h"
+#include "components/user_manager/user_id.h"
 #include "components/user_manager/user_manager.h"
 #include "content/public/browser/browser_thread.h"
 #include "content/public/browser/user_metrics.h"
@@ -55,7 +56,7 @@ bool StoreSupervisedUserFiles(const std::string& token,
 
 SupervisedUserCreationControllerNew::SupervisedUserCreationControllerNew(
     SupervisedUserCreationControllerNew::StatusConsumer* consumer,
-    const std::string& manager_id)
+    const user_manager::UserID& manager_id)
     : SupervisedUserCreationController(consumer),
       stage_(STAGE_INITIAL),
       weak_factory_(this) {
@@ -67,7 +68,7 @@ SupervisedUserCreationControllerNew::SupervisedUserCreationControllerNew(
 SupervisedUserCreationControllerNew::~SupervisedUserCreationControllerNew() {}
 
 SupervisedUserCreationControllerNew::UserCreationContext::
-    UserCreationContext() {}
+    UserCreationContext() : manager_id(std::string(), std::string()), local_user_id(std::string(), std::string()) {}

[Denis Kuznetsov (DE-MUC), 2015/06/10 16:50:46]

EmptyGaiaID() ?

 
 SupervisedUserCreationControllerNew::UserCreationContext::
     ~UserCreationContext() {}
@@ -155,7 +156,7 @@ void SupervisedUserCreationControllerNew::StartCreationImpl() {
   creation_context_->local_user_id = manager->GenerateUserId();
   if (creation_context_->creation_type == NEW_USER) {
     creation_context_->sync_user_id =
-        SupervisedUserRegistrationUtility::GenerateNewSupervisedUserId();
+        SupervisedUserRegistrationUtility::GenerateNewSupervisedUserId().GetUserEmail();
   }
 
   manager->SetCreationTransactionUserId(creation_context_->local_user_id);
@@ -329,7 +330,7 @@ void SupervisedUserCreationControllerNew::OnAddKeySuccess() {
 
   // Registration utility will update user data if user already exist.
   creation_context_->registration_utility->Register(
-      creation_context_->sync_user_id,
+      user_manager::UserID::FromUserEmail(creation_context_->sync_user_id),
       info,
       base::Bind(&SupervisedUserCreationControllerNew::RegistrationCallback,
                  weak_factory_.GetWeakPtr()));
@@ -414,7 +415,7 @@ void SupervisedUserCreationControllerNew::CancelCreation() {
   chrome::AttemptUserExit();
 }
 
-std::string SupervisedUserCreationControllerNew::GetSupervisedUserId() {
+const user_manager::UserID& SupervisedUserCreationControllerNew::GetSupervisedUserId() const {
   DCHECK(creation_context_);
   return creation_context_->local_user_id;
 }