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

chrome/browser/profiles/profile_manager.cc

Index: chrome/browser/profiles/profile_manager.cc
diff --git a/chrome/browser/profiles/profile_manager.cc b/chrome/browser/profiles/profile_manager.cc
index 408917b51b3da022007259e6433faaca16fc7158..a570924f160d9b209b6df2ee5c872cb07edbf2db 100644
--- a/chrome/browser/profiles/profile_manager.cc
+++ b/chrome/browser/profiles/profile_manager.cc
@@ -393,7 +393,7 @@ void ProfileManager::CreateProfileAsync(
     const CreateCallback& callback,
     const base::string16& name,
     const base::string16& icon_url,
-    const std::string& supervised_user_id) {
+    const user_manager::UserID& supervised_user_id) {
   DCHECK_CURRENTLY_ON(BrowserThread::UI);
   TRACE_EVENT1("browser,startup",
                "ProfileManager::CreateProfileAsync",
@@ -574,7 +574,7 @@ base::FilePath ProfileManager::CreateMultiProfileAsync(
     const base::string16& name,
     const base::string16& icon_url,
     const CreateCallback& callback,
-    const std::string& supervised_user_id) {
+    const user_manager::UserID& supervised_user_id) {
   DCHECK_CURRENTLY_ON(BrowserThread::UI);
 
   ProfileManager* profile_manager = g_browser_process->profile_manager();
@@ -695,7 +695,7 @@ void ProfileManager::ScheduleProfileForDeletion(
                                   callback),
                        new_profile_name,
                        new_avatar_url,
-                       std::string());
+                       user_manager::UserID(std::string(), std::string()));

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

EmptyUserID

 
     ProfileMetrics::LogProfileAddNewUser(
         ProfileMetrics::ADD_NEW_USER_LAST_DELETED);
@@ -718,7 +718,7 @@ void ProfileManager::ScheduleProfileForDeletion(
                                   callback),
                        base::string16(),
                        base::string16(),
-                       std::string());
+                       user_manager::UserID(std::string(), std::string()));

[Denis Kuznetsov (DE-MUC), 2015/06/10 16:50:44]

EmtpyUserID

     return;
   }
 #endif  // defined(OS_MACOSX)
@@ -796,7 +796,7 @@ void ProfileManager::InitProfileUserPrefs(Profile* profile) {
 
   size_t avatar_index;
   std::string profile_name;
-  std::string supervised_user_id;
+  user_manager::UserID supervised_user_id = user_manager::UserID(std::string(), std::string());

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

EmptyUserID

   if (profile->IsGuestSession()) {
     profile_name = l10n_util::GetStringUTF8(IDS_PROFILES_GUEST_PROFILE_NAME);
     avatar_index = 0;
@@ -841,13 +841,13 @@ void ProfileManager::InitProfileUserPrefs(Profile* profile) {
 #endif
       command_line->HasSwitch(switches::kSupervisedUserId);
   if (force_supervised_user_id) {
-    supervised_user_id =
-        command_line->GetSwitchValueASCII(switches::kSupervisedUserId);
+    supervised_user_id = user_manager::UserID::FromUserEmail(
+        command_line->GetSwitchValueASCII(switches::kSupervisedUserId));
   }
   if (force_supervised_user_id ||
       !profile->GetPrefs()->HasPrefPath(prefs::kSupervisedUserId)) {
     profile->GetPrefs()->SetString(prefs::kSupervisedUserId,
-                                   supervised_user_id);
+                                   supervised_user_id.GetUserEmail());
   }
 }
 
@@ -1310,8 +1310,8 @@ void ProfileManager::AddProfileToCache(Profile* profile) {
   size_t icon_index = profile->GetPrefs()->GetInteger(
       prefs::kProfileAvatarIndex);
 
-  std::string supervised_user_id =
-      profile->GetPrefs()->GetString(prefs::kSupervisedUserId);
+  const user_manager::UserID& supervised_user_id =
+      user_manager::UserID::FromUserEmail(profile->GetPrefs()->GetString(prefs::kSupervisedUserId));
 
   cache.AddProfileToCache(profile->GetPath(),
                           profile_name,