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

chrome/browser/chromeos/login/users/chrome_user_manager_impl.h

Index: chrome/browser/chromeos/login/users/chrome_user_manager_impl.h
diff --git a/chrome/browser/chromeos/login/users/chrome_user_manager_impl.h b/chrome/browser/chromeos/login/users/chrome_user_manager_impl.h
index d7794917173bb3986d9a97dd90304bf1bd562d52..85e47311af0f935cf5d4b9ec8c70aa35c634c4fd 100644
--- a/chrome/browser/chromeos/login/users/chrome_user_manager_impl.h
+++ b/chrome/browser/chromeos/login/users/chrome_user_manager_impl.h
@@ -68,12 +68,12 @@ class ChromeUserManagerImpl
   // UserManagerInterface implementation:
   BootstrapManager* GetBootstrapManager() override;
   MultiProfileUserController* GetMultiProfileUserController() override;
-  UserImageManager* GetUserImageManager(const std::string& user_id) override;
+  UserImageManager* GetUserImageManager(const user_manager::UserID& user_id) override;
   SupervisedUserManager* GetSupervisedUserManager() override;
   UserFlow* GetCurrentUserFlow() const override;
-  UserFlow* GetUserFlow(const std::string& user_id) const override;
-  void SetUserFlow(const std::string& user_id, UserFlow* flow) override;
-  void ResetUserFlow(const std::string& user_id) override;
+  UserFlow* GetUserFlow(const user_manager::UserID& user_id) const override;
+  void SetUserFlow(const user_manager::UserID& user_id, UserFlow* flow) override;
+  void ResetUserFlow(const user_manager::UserID& user_id) override;
 
   // UserManager implementation:
   void Shutdown() override;
@@ -83,13 +83,13 @@ class ChromeUserManagerImpl
   user_manager::UserList GetUnlockUsers() const override;
   void SessionStarted() override;
   void SaveUserOAuthStatus(
-      const std::string& user_id,
+      const user_manager::UserID& user_id,
       user_manager::User::OAuthTokenStatus oauth_token_status) override;
-  void SaveUserDisplayName(const std::string& user_id,
+  void SaveUserDisplayName(const user_manager::UserID& user_id,
                            const base::string16& display_name) override;
   bool CanCurrentUserLock() const override;
   bool IsUserNonCryptohomeDataEphemeral(
-      const std::string& user_id) const override;
+      const user_manager::UserID& user_id) const override;
   bool AreSupervisedUsersAllowed() const override;
 
   // content::NotificationObserver implementation.
@@ -99,15 +99,15 @@ class ChromeUserManagerImpl
 
   // policy::CloudExternalDataPolicyObserver::Delegate:
   void OnExternalDataSet(const std::string& policy,
-                         const std::string& user_id) override;
+                         const user_manager::UserID& user_id) override;
   void OnExternalDataCleared(const std::string& policy,
-                             const std::string& user_id) override;
+                             const user_manager::UserID& user_id) override;
   void OnExternalDataFetched(const std::string& policy,
-                             const std::string& user_id,
+                             const user_manager::UserID& user_id,
                              scoped_ptr<std::string> data) override;
 
   // policy::DeviceLocalAccountPolicyService::Observer implementation.
-  void OnPolicyUpdated(const std::string& user_id) override;
+  void OnPolicyUpdated(const user_manager::UserID& user_id) override;
   void OnDeviceLocalAccountsChanged() override;
 
   void StopPolicyObserverForTesting();
@@ -119,7 +119,7 @@ class ChromeUserManagerImpl
   const std::string& GetApplicationLocale() const override;
   PrefService* GetLocalState() const override;
   void HandleUserOAuthTokenStatusChange(
-      const std::string& user_id,
+      const user_manager::UserID& user_id,
       user_manager::User::OAuthTokenStatus status) const override;
   bool IsEnterpriseManaged() const override;
   void LoadPublicAccounts(std::set<std::string>* users_set) override;
@@ -129,21 +129,21 @@ class ChromeUserManagerImpl
   void PerformPreUserListLoadingActions() override;
   void PerformPostUserListLoadingActions() override;
   void PerformPostUserLoggedInActions(bool browser_restart) override;
-  void RemoveNonCryptohomeData(const std::string& user_id) override;
-  void RemoveUserInternal(const std::string& user_email,
+  void RemoveNonCryptohomeData(const user_manager::UserID& user_id) override;
+  void RemoveUserInternal(const user_manager::UserID& user_id,
                           user_manager::RemoveUserDelegate* delegate) override;
-  bool IsDemoApp(const std::string& user_id) const override;
-  bool IsKioskApp(const std::string& user_id) const override;
+  bool IsDemoApp(const user_manager::UserID& user_id) const override;
+  bool IsKioskApp(const user_manager::UserID& user_id) const override;
   bool IsPublicAccountMarkedForRemoval(
-      const std::string& user_id) const override;
+      const user_manager::UserID& user_id) const override;
   void DemoAccountLoggedIn() override;
   void GuestUserLoggedIn() override;
   void KioskAppLoggedIn(const std::string& app_id) override;
   void PublicAccountUserLoggedIn(user_manager::User* user) override;
-  void RegularUserLoggedIn(const std::string& user_id) override;
-  void RegularUserLoggedInAsEphemeral(const std::string& user_id) override;
-  void SupervisedUserLoggedIn(const std::string& user_id) override;
-  bool HasPendingBootstrap(const std::string& user_id) const override;
+  void RegularUserLoggedIn(const user_manager::UserID& user_id) override;
+  void RegularUserLoggedInAsEphemeral(const user_manager::UserID& user_id) override;
+  void SupervisedUserLoggedIn(const user_manager::UserID& user_id) override;
+  bool HasPendingBootstrap(const user_manager::UserID& user_id) const override;
 
  private:
   friend class SupervisedUserManagerImpl;
@@ -151,7 +151,7 @@ class ChromeUserManagerImpl
   friend class WallpaperManager;
   friend class WallpaperManagerTest;
 
-  typedef base::hash_map<std::string, linked_ptr<UserImageManager> >
+  typedef base::hash_map<user_manager::UserID, linked_ptr<UserImageManager> >
       UserImageManagerMap;
 
   ChromeUserManagerImpl();
@@ -173,7 +173,7 @@ class ChromeUserManagerImpl
   // data for that account is not removed immediately but marked as pending
   // removal after logout.
   void CleanUpPublicAccountNonCryptohomeData(
-      const std::vector<std::string>& old_public_accounts);
+      const std::vector<user_manager::UserID>& old_public_accounts);
 
   // Replaces the list of public accounts with those found in
   // |device_local_accounts|. Ensures that data belonging to accounts no longer
@@ -185,7 +185,7 @@ class ChromeUserManagerImpl
 
   // Updates the display name for public account |username| from policy settings
   // associated with that username.
-  void UpdatePublicAccountDisplayName(const std::string& user_id);
+  void UpdatePublicAccountDisplayName(const user_manager::UserID& user_id);
 
   // Notifies the UI about a change to the user list.
   void NotifyUserListChanged();
@@ -194,10 +194,10 @@ class ChromeUserManagerImpl
   UserFlow* GetDefaultUserFlow() const;
 
   // MultiProfileUserControllerDelegate implementation:
-  void OnUserNotAllowed(const std::string& user_email) override;
+  void OnUserNotAllowed(const user_manager::UserID& user_id) override;
 
   // BootstrapManager::Delegate implementation:
-  void RemovePendingBootstrapUser(const std::string& user_id) override;
+  void RemovePendingBootstrapUser(const user_manager::UserID& user_id) override;
 
   // Update the number of users.
   void UpdateNumberOfUsers();
@@ -223,13 +223,12 @@ class ChromeUserManagerImpl
   // Session length limiter.
   scoped_ptr<SessionLengthLimiter> session_length_limiter_;
 
-  typedef std::map<std::string, UserFlow*> FlowMap;
+  typedef std::map<user_manager::UserID, UserFlow*> FlowMap;
 
   // Lazy-initialized default flow.
   mutable scoped_ptr<UserFlow> default_flow_;
 
-  // Specific flows by user e-mail. Keys should be canonicalized before
-  // access.
+  // Specific flows by user id.
   FlowMap specific_flows_;
 
   scoped_ptr<CrosSettings::ObserverSubscription> local_accounts_subscription_;