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

chrome/browser/chromeos/login/easy_unlock/easy_unlock_key_manager.h

 // Copyright 2014 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_CHROMEOS_LOGIN_EASY_UNLOCK_EASY_UNLOCK_KEY_MANAGER_H_
 #define CHROME_BROWSER_CHROMEOS_LOGIN_EASY_UNLOCK_EASY_UNLOCK_KEY_MANAGER_H_
 
 #include <deque>
 #include <map>
 #include <string>
 
 #include "base/callback.h"
 #include "base/macros.h"
 #include "base/memory/weak_ptr.h"
 #include "base/stl_util.h"
 #include "chrome/browser/chromeos/login/easy_unlock/easy_unlock_get_keys_operation.h"
 #include "chrome/browser/chromeos/login/easy_unlock/easy_unlock_refresh_keys_operation.h"
 #include "chrome/browser/chromeos/login/easy_unlock/easy_unlock_types.h"
 
 namespace base {
 class DictionaryValue;
 class ListValue;
 }
 
+namespace user_manager {
+class UserID;
+}
+
 namespace chromeos {
 
 class UserContext;
 
 // A class to manage Easy unlock cryptohome keys.
 class EasyUnlockKeyManager {
  public:
   typedef EasyUnlockRefreshKeysOperation::RefreshKeysCallback
       RefreshKeysCallback;
   typedef EasyUnlockGetKeysOperation::GetKeysCallback GetDeviceDataListCallback;
@@ skipping 12 matching lines @@
   // |user_context|.
   void GetDeviceDataList(const UserContext& user_context,
                          const GetDeviceDataListCallback& callback);
 
   // Helpers to convert between DeviceData and remote device dictionary.
   // DeviceDataToRemoteDeviceDictionary fills the remote device dictionary and
   // always succeeds. RemoteDeviceDictionaryToDeviceData returns false if the
   // conversion fails (missing required propery). Note that
   // EasyUnlockDeviceKeyData contains a sub set of the remote device dictionary.
   static void DeviceDataToRemoteDeviceDictionary(
-      const std::string& user_id,
+      const user_manager::UserID& user_id,
       const EasyUnlockDeviceKeyData& data,
       base::DictionaryValue* dict);
   static bool RemoteDeviceDictionaryToDeviceData(
       const base::DictionaryValue& dict,
       EasyUnlockDeviceKeyData* data);
 
   // Helpers to convert between EasyUnlockDeviceKeyDataList and remote devices
   // ListValue.
   static void DeviceDataListToRemoteDeviceList(
-      const std::string& user_id,
+      const user_manager::UserID& user_id,
       const EasyUnlockDeviceKeyDataList& data_list,
       base::ListValue* device_list);
   static bool RemoteDeviceListToDeviceDataList(
       const base::ListValue& device_list,
       EasyUnlockDeviceKeyDataList* data_list);
 
   // Gets key label for the given key index.
   static std::string GetKeyLabel(size_t key_index);
 
  private:
@@ skipping 37 matching lines @@
   scoped_ptr<EasyUnlockGetKeysOperation> pending_read_operation_;
 
   base::WeakPtrFactory<EasyUnlockKeyManager> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(EasyUnlockKeyManager);
 };
 
 }  // namespace chromeos
 
 #endif  // CHROME_BROWSER_CHROMEOS_LOGIN_EASY_UNLOCK_EASY_UNLOCK_KEY_MANAGER_H_