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

chrome/browser/chromeos/policy/user_cloud_policy_manager_chromeos.h

 // Copyright (c) 2012 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_POLICY_USER_CLOUD_POLICY_MANAGER_CHROMEOS_H_
 #define CHROME_BROWSER_CHROMEOS_POLICY_USER_CLOUD_POLICY_MANAGER_CHROMEOS_H_
 
 #include <string>
 
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
 #include "base/files/file_path.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/time/time.h"
 #include "base/timer/timer.h"
 #include "components/keyed_service/core/keyed_service.h"
 #include "components/policy/core/common/cloud/cloud_policy_client.h"
 #include "components/policy/core/common/cloud/cloud_policy_constants.h"
 #include "components/policy/core/common/cloud/cloud_policy_manager.h"
 #include "components/policy/core/common/cloud/cloud_policy_service.h"
+#include "components/user_manager/user_id.h"
 
 class GoogleServiceAuthError;
 class PrefService;
 
 namespace base {
 class SequencedTaskRunner;
 }
 
 namespace net {
 class URLRequestContextGetter;
 }
 
+namespace user_manager {
+class UserID;
+}
+
 namespace policy {
 
 class CloudExternalDataManager;
 class DeviceManagementService;
 class PolicyOAuth2TokenFetcher;
 class WildcardLoginChecker;
 
 // UserCloudPolicyManagerChromeOS implements logic for initializing user policy
 // on Chrome OS.
 class UserCloudPolicyManagerChromeOS : public CloudPolicyManager,
@@ skipping 36 matching lines @@
   // to this method once available.
   // The |access_token| can then be used to authenticate the registration
   // request to the DMServer.
   void OnAccessTokenAvailable(const std::string& access_token);
 
   // Returns true if the underlying CloudPolicyClient is already registered.
   bool IsClientRegistered() const;
 
   // Indicates a wildcard login check should be performed once an access token
   // is available.
-  void EnableWildcardLoginCheck(const std::string& username);
+  void EnableWildcardLoginCheck(const user_manager::UserID& user_id);
 
   // ConfigurationPolicyProvider:
   void Shutdown() override;
   bool IsInitializationComplete(PolicyDomain domain) const override;
 
   // CloudPolicyService::Observer:
   void OnInitializationCompleted(CloudPolicyService* service) override;
 
   // CloudPolicyClient::Observer:
   void OnPolicyFetched(CloudPolicyClient* client) override;
@@ skipping 34 matching lines @@
 
   void StartRefreshSchedulerIfReady();
 
   // Owns the store, note that CloudPolicyManager just keeps a plain pointer.
   scoped_ptr<CloudPolicyStore> store_;
 
   // Manages external data referenced by policies.
   scoped_ptr<CloudExternalDataManager> external_data_manager_;
 
   // Username for the wildcard login check if applicable, empty otherwise.
-  std::string wildcard_username_;
+  user_manager::UserID wildcard_user_id_;
 
   // Path where policy for components will be cached.
   base::FilePath component_policy_cache_path_;
 
   // Whether to wait for a policy fetch to complete before reporting
   // IsInitializationComplete().
   bool wait_for_policy_fetch_;
 
   // A timer that puts a hard limit on the maximum time to wait for the initial
   // policy fetch.
@@ skipping 18 matching lines @@
   base::Time time_init_completed_;
   base::Time time_token_available_;
   base::Time time_client_registered_;
 
   DISALLOW_COPY_AND_ASSIGN(UserCloudPolicyManagerChromeOS);
 };
 
 }  // namespace policy
 
 #endif  // CHROME_BROWSER_CHROMEOS_POLICY_USER_CLOUD_POLICY_MANAGER_CHROMEOS_H_