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

chrome/browser/chromeos/extensions/file_manager/private_api_misc.cc

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/chromeos/extensions/file_manager/private_api_misc.h"
 
 #include <set>
 #include <vector>
 
 #include "ash/frame/frame_util.h"
@@ skipping 87 matching lines @@
 
   return result_profiles;
 }
 }  // namespace
 
 bool FileManagerPrivateLogoutUserForReauthenticationFunction::RunSync() {
   const user_manager::User* user =
       chromeos::ProfileHelper::Get()->GetUserByProfile(GetProfile());
   if (user) {
     user_manager::UserManager::Get()->SaveUserOAuthStatus(
-        user->email(), user_manager::User::OAUTH2_TOKEN_STATUS_INVALID);
+        user->GetUserID(), user_manager::User::OAUTH2_TOKEN_STATUS_INVALID);
   }
 
   chrome::AttemptUserExit();
   return true;
 }
 
 bool FileManagerPrivateGetPreferencesFunction::RunSync() {
   api::file_manager_private::Preferences result;
   const PrefService* const service = GetProfile()->GetPrefs();
 
@@ skipping 206 matching lines @@
 }
 
 bool FileManagerPrivateGetProfilesFunction::RunSync() {
   const std::vector<linked_ptr<api::file_manager_private::ProfileInfo> >&
       profiles = GetLoggedInProfileInfoList();
 
   // Obtains the display profile ID.
   AppWindow* const app_window = GetCurrentAppWindow(this);
   chrome::MultiUserWindowManager* const window_manager =
       chrome::MultiUserWindowManager::GetInstance();
-  const std::string current_profile_id =
+  const user_manager::UserID current_profile_id =
       multi_user_util::GetUserIDFromProfile(GetProfile());
-  const std::string display_profile_id =
+  const user_manager::UserID display_profile_id =
       window_manager && app_window ? window_manager->GetUserPresentingWindow(
                                          app_window->GetNativeWindow())
-                                   : "";
+                                   : user_manager::UserID(std::string(), std::string());

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

EmptyUserID()?

 
   results_ = api::file_manager_private::GetProfiles::Results::Create(
       profiles,
-      current_profile_id,
-      display_profile_id.empty() ? current_profile_id : display_profile_id);
+      current_profile_id.GetUserEmail(),
+      display_profile_id.empty() ? current_profile_id.GetUserEmail() : display_profile_id.GetUserEmail());
   return true;
 }
 
 bool FileManagerPrivateOpenInspectorFunction::RunSync() {
   using extensions::api::file_manager_private::OpenInspector::Params;
   const scoped_ptr<Params> params(Params::Create(*args_));
   EXTENSION_FUNCTION_VALIDATE(params);
 
   switch (params->type) {
     case extensions::api::file_manager_private::INSPECTION_TYPE_NORMAL:
@@ skipping 184 matching lines @@
     base::File::Error result) {
   if (result != base::File::FILE_OK) {
     Respond(Error("Failed to complete configuration."));
     return;
   }
 
   Respond(NoArguments());
 }
 
 }  // namespace extensions