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

chrome/browser/supervised_user/legacy/supervised_user_registration_utility.cc

Index: chrome/browser/supervised_user/legacy/supervised_user_registration_utility.cc
diff --git a/chrome/browser/supervised_user/legacy/supervised_user_registration_utility.cc b/chrome/browser/supervised_user/legacy/supervised_user_registration_utility.cc
index 5242fd63e96a717e0fd220107d3db88d9e04997c..8a377360f97d61f52cf715c6d70738f507e94371 100644
--- a/chrome/browser/supervised_user/legacy/supervised_user_registration_utility.cc
+++ b/chrome/browser/supervised_user/legacy/supervised_user_registration_utility.cc
@@ -27,6 +27,7 @@
 #include "components/signin/core/browser/profile_oauth2_token_service.h"
 #include "components/signin/core/browser/signin_client.h"
 #include "components/signin/core/browser/signin_manager.h"
+#include "components/user_manager/user_id.h"
 #include "content/public/browser/browser_thread.h"
 #include "google_apis/gaia/gaia_urls.h"
 #include "google_apis/gaia/google_service_auth_error.h"
@@ -59,13 +60,13 @@ class SupervisedUserRegistrationUtilityImpl
   // the user and his avatar. |callback| is called with the result of the
   // registration. We use the info here and not the profile, because on Chrome
   // OS the profile of the supervised user does not yet exist.
-  void Register(const std::string& supervised_user_id,
+  void Register(const user_manager::UserID& supervised_user_id,
                 const SupervisedUserRegistrationInfo& info,
                 const RegistrationCallback& callback) override;
 
   // SupervisedUserSyncServiceObserver:
   void OnSupervisedUserAcknowledged(
-      const std::string& supervised_user_id) override;
+      const user_manager::UserID& supervised_user_id) override;
   void OnSupervisedUsersSyncingStopped() override;
   void OnSupervisedUsersChanged() override;
 
@@ -108,7 +109,7 @@ class SupervisedUserRegistrationUtilityImpl
   // A |KeyedService| owned by the custodian profile.
   SupervisedUserSharedSettingsService* supervised_user_shared_settings_service_;
 
-  std::string pending_supervised_user_id_;
+  user_manager::UserID pending_supervised_user_id_;
   std::string pending_supervised_user_token_;
   bool pending_supervised_user_acknowledged_;
   bool is_existing_supervised_user_;
@@ -178,10 +179,10 @@ SupervisedUserRegistrationUtility::Create(Profile* profile) {
 }
 
 // static
-std::string SupervisedUserRegistrationUtility::GenerateNewSupervisedUserId() {
-  std::string new_supervised_user_id;
-  base::Base64Encode(base::RandBytesAsString(8), &new_supervised_user_id);
-  return new_supervised_user_id;
+user_manager::UserID SupervisedUserRegistrationUtility::GenerateNewSupervisedUserId() {
+  std::string new_supervised_user_id_str;
+  base::Base64Encode(base::RandBytesAsString(8), &new_supervised_user_id_str);
+  return user_manager::UserID::FromUserEmail(new_supervised_user_id_str);
 }
 
 // static
@@ -216,6 +217,7 @@ SupervisedUserRegistrationUtilityImpl::SupervisedUserRegistrationUtilityImpl(
       token_fetcher_(token_fetcher.Pass()),
       supervised_user_sync_service_(service),
       supervised_user_shared_settings_service_(shared_settings_service),
+      pending_supervised_user_id_(std::string(), std::string()),
       pending_supervised_user_acknowledged_(false),
       is_existing_supervised_user_(false),
       avatar_updated_(false),
@@ -230,7 +232,7 @@ SupervisedUserRegistrationUtilityImpl::
 }
 
 void SupervisedUserRegistrationUtilityImpl::Register(
-    const std::string& supervised_user_id,
+    const user_manager::UserID& supervised_user_id,
     const SupervisedUserRegistrationInfo& info,
     const RegistrationCallback& callback) {
   DCHECK(pending_supervised_user_id_.empty());
@@ -240,7 +242,7 @@ void SupervisedUserRegistrationUtilityImpl::Register(
   bool need_password_update = !info.password_data.empty();
   const base::DictionaryValue* dict =
       prefs_->GetDictionary(prefs::kSupervisedUsers);
-  is_existing_supervised_user_ = dict->HasKey(supervised_user_id);
+  is_existing_supervised_user_ = dict->HasKey(supervised_user_id.GetUserEmail());
   if (!is_existing_supervised_user_) {
     supervised_user_sync_service_->AddSupervisedUser(
         pending_supervised_user_id_,
@@ -252,7 +254,7 @@ void SupervisedUserRegistrationUtilityImpl::Register(
   } else {
     const base::DictionaryValue* value = NULL;
     bool success =
-        dict->GetDictionaryWithoutPathExpansion(supervised_user_id, &value);
+        dict->GetDictionaryWithoutPathExpansion(supervised_user_id.GetUserEmail(), &value);
     DCHECK(success);
     std::string key;
     bool need_keys = !info.password_signature_key.empty() ||
@@ -291,12 +293,12 @@ void SupervisedUserRegistrationUtilityImpl::Register(
   const char* kAvatarKey = supervised_users::kChromeAvatarIndex;
 #endif
   supervised_user_shared_settings_service_->SetValue(
-      pending_supervised_user_id_, kAvatarKey,
+      pending_supervised_user_id_.GetUserEmail(), kAvatarKey,
       base::FundamentalValue(info.avatar_index));
   if (need_password_update) {
     password_update_.reset(new SupervisedUserSharedSettingsUpdate(
         supervised_user_shared_settings_service_,
-        pending_supervised_user_id_,
+        pending_supervised_user_id_.GetUserEmail(),
         supervised_users::kChromeOSPasswordData,
         scoped_ptr<base::Value>(info.password_data.DeepCopy()),
         base::Bind(
@@ -320,8 +322,8 @@ void SupervisedUserRegistrationUtilityImpl::CancelPendingRegistration() {
 }
 
 void SupervisedUserRegistrationUtilityImpl::OnSupervisedUserAcknowledged(
-    const std::string& supervised_user_id) {
-  DCHECK_EQ(pending_supervised_user_id_, supervised_user_id);
+    const user_manager::UserID& supervised_user_id) {
+  DCHECK(pending_supervised_user_id_ == supervised_user_id);
   DCHECK(!pending_supervised_user_acknowledged_);
   pending_supervised_user_acknowledged_ = true;
   CompleteRegistrationIfReady();