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

chrome/browser/signin/easy_unlock_app_manager.h

 // Copyright 2015 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.
 
 #ifndef CHROME_BROWSER_SIGNIN_EASY_UNLOCK_APP_MANAGER_H_
 #define CHROME_BROWSER_SIGNIN_EASY_UNLOCK_APP_MANAGER_H_
 
 #include <string>
 
 #include "base/callback.h"
 #include "base/files/file_path.h"
 #include "base/macros.h"
 
 namespace extensions {
 class ExtensionSystem;
 }
 
+namespace user_manager {
+class UserID;
+}
+
 // Used to manage Easy Unlock app's lifetime and to dispatch events to the app.
 // It's main purpose is to abstract extension system from the rest of easy
 // unlock code.
 class EasyUnlockAppManager {
  public:
   virtual ~EasyUnlockAppManager();
 
   // Creates EasyUnlockAppManager object that should be used in production.
   static scoped_ptr<EasyUnlockAppManager> Create(
       extensions::ExtensionSystem* extension_system,
@@ skipping 11 matching lines @@
   // Loads Easy Unlock app.
   virtual void LoadApp() = 0;
 
   // Disables Easy Unlock app.
   virtual void DisableAppIfLoaded() = 0;
 
   // Reloads Easy Unlock app.
   virtual void ReloadApp() = 0;
 
   // Sends easyUnlockPrivate.onUserInfoUpdate event to Easy Unlock app.
-  virtual bool SendUserUpdatedEvent(const std::string& user_id,
+  virtual bool SendUserUpdatedEvent(const user_manager::UserID& user_id,
                                     bool is_logged_in,
                                     bool data_ready) = 0;
 
   // Sends screenlockPrivate.onAuthAttempted event to Easy Unlock app.
   virtual bool SendAuthAttemptEvent() = 0;
 };
 
 #endif  // CHROME_BROWSER_SIGNIN_EASY_UNLOCK_APP_MANAGER_H_