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

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

Index: chrome/browser/chromeos/extensions/file_manager/private_api_misc.cc
diff --git a/chrome/browser/chromeos/extensions/file_manager/private_api_misc.cc b/chrome/browser/chromeos/extensions/file_manager/private_api_misc.cc
index 6cbc10bbf30ddd12a403e6c3fa9454ddae0d2193..031b39c1245a10fb11268b8648d27e400db75479 100644
--- a/chrome/browser/chromeos/extensions/file_manager/private_api_misc.cc
+++ b/chrome/browser/chromeos/extensions/file_manager/private_api_misc.cc
@@ -105,7 +105,7 @@ bool FileManagerPrivateLogoutUserForReauthenticationFunction::RunSync() {
       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();
@@ -332,17 +332,17 @@ bool FileManagerPrivateGetProfilesFunction::RunSync() {
   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;
 }