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

chrome/browser/chromeos/login/signin/auth_sync_observer.cc

Index: chrome/browser/chromeos/login/signin/auth_sync_observer.cc
diff --git a/chrome/browser/chromeos/login/signin/auth_sync_observer.cc b/chrome/browser/chromeos/login/signin/auth_sync_observer.cc
index 8fa574959b7f0d25a03e412db313ca62c041ae3c..b174b190bfeb6bce8f2f4326bc192c835158add5 100644
--- a/chrome/browser/chromeos/login/signin/auth_sync_observer.cc
+++ b/chrome/browser/chromeos/login/signin/auth_sync_observer.cc
@@ -62,14 +62,14 @@ void AuthSyncObserver::OnStateChanged() {
     // TODO(nkostylev): Remove after crosbug.com/25978 is implemented.
     LOG(WARNING) << "Invalidate OAuth token because of a sync error: "
                  << sync_service->GetAuthError().ToString();
-    std::string email = user->email();
-    DCHECK(!email.empty());
+    user_manager::UserID user_id = user->GetUserID();

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

auto

+    DCHECK(!user_id.empty());
     // TODO(nkostyelv): Change observer after active user has changed.
     user_manager::User::OAuthTokenStatus old_status =
         user->oauth_token_status();
     user_manager::UserManager::Get()->SaveUserOAuthStatus(
-        email, user_manager::User::OAUTH2_TOKEN_STATUS_INVALID);
-    RecordReauthReason(email, ReauthReason::SYNC_FAILED);
+        user_id, user_manager::User::OAUTH2_TOKEN_STATUS_INVALID);
+    RecordReauthReason(user_id, ReauthReason::SYNC_FAILED);
     if (user->GetType() == user_manager::USER_TYPE_SUPERVISED &&
         old_status != user_manager::User::OAUTH2_TOKEN_STATUS_INVALID) {
        // Attempt to restore token from file.
@@ -89,7 +89,7 @@ void AuthSyncObserver::OnStateChanged() {
       LOG(ERROR) <<
           "Got an incorrectly invalidated token case, restoring token status.";
       user_manager::UserManager::Get()->SaveUserOAuthStatus(
-          user->email(), user_manager::User::OAUTH2_TOKEN_STATUS_VALID);
+          user->GetUserID(), user_manager::User::OAUTH2_TOKEN_STATUS_VALID);
        content::RecordAction(
            base::UserMetricsAction("ManagedUsers_Chromeos_Sync_Recovered"));
     }