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

chrome/browser/chromeos/settings/device_settings_service.cc

Index: chrome/browser/chromeos/settings/device_settings_service.cc
diff --git a/chrome/browser/chromeos/settings/device_settings_service.cc b/chrome/browser/chromeos/settings/device_settings_service.cc
index a696102cd0e141a4895e8c62e05c39a66dea12b3..9d1fac32190625fb7409d2f1ba7cac9e720d3ba2 100644
--- a/chrome/browser/chromeos/settings/device_settings_service.cc
+++ b/chrome/browser/chromeos/settings/device_settings_service.cc
@@ -71,6 +71,7 @@ DeviceSettingsService* DeviceSettingsService::Get() {
 DeviceSettingsService::DeviceSettingsService()
     : session_manager_client_(NULL),
       store_status_(STORE_SUCCESS),
+      user_id_(std::string(), std::string()),
       load_retries_left_(kMaxLoadRetries),
       weak_factory_(this) {
 }
@@ -150,21 +151,21 @@ bool DeviceSettingsService::HasPrivateOwnerKey() {
 }
 
 void DeviceSettingsService::InitOwner(
-    const std::string& username,
+    const user_manager::UserID& user_id,
     const base::WeakPtr<ownership::OwnerSettingsService>&
         owner_settings_service) {
-  // When InitOwner() is called twice with the same |username| it's
+  // When InitOwner() is called twice with the same |user_id| it's
   // worth to reload settings since owner key may become available.
-  if (!username_.empty() && username_ != username)
+  if (!user_id_.empty() && user_id_ != user_id)
     return;
-  username_ = username;
+  user_id_ = user_id;
   owner_settings_service_ = owner_settings_service;
 
   EnsureReload(true);
 }
 
-const std::string& DeviceSettingsService::GetUsername() const {
-  return username_;
+const user_manager::UserID& DeviceSettingsService::GetUserID() const {
+  return user_id_;
 }
 
 ownership::OwnerSettingsService*