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

components/user_manager/user_manager_base.h

Index: components/user_manager/user_manager_base.h
diff --git a/components/user_manager/user_manager_base.h b/components/user_manager/user_manager_base.h
index d8454efa620387eddf02c6e8fa3bc3cc7a06d9ea..ca6d8dc258f7f06987ac911a2bfaa01c9e29ff37 100644
--- a/components/user_manager/user_manager_base.h
+++ b/components/user_manager/user_manager_base.h
@@ -51,37 +51,37 @@ class USER_MANAGER_EXPORT UserManagerBase : public UserManager {
   const UserList& GetUsers() const override;
   const UserList& GetLoggedInUsers() const override;
   const UserList& GetLRULoggedInUsers() const override;
-  const std::string& GetOwnerEmail() const override;
-  void UserLoggedIn(const std::string& user_id,
+  const UserID& GetOwnerID() const override;
+  void UserLoggedIn(const UserID& user_id,
                     const std::string& user_id_hash,
                     bool browser_restart) override;
-  void SwitchActiveUser(const std::string& user_id) override;
+  void SwitchActiveUser(const UserID& user_id) override;
   void SwitchToLastActiveUser() override;
   void SessionStarted() override;
-  void RemoveUser(const std::string& user_id,
+  void RemoveUser(const UserID& user_id,
                   RemoveUserDelegate* delegate) override;
-  void RemoveUserFromList(const std::string& user_id) override;
-  bool IsKnownUser(const std::string& user_id) const override;
-  const User* FindUser(const std::string& user_id) const override;
-  User* FindUserAndModify(const std::string& user_id) override;
+  void RemoveUserFromList(const UserID& user_id) override;
+  bool IsKnownUser(const UserID& user_id) const override;
+  const User* FindUser(const UserID& user_id) const override;
+  User* FindUserAndModify(const UserID& user_id) override;
   const User* GetLoggedInUser() const override;
   User* GetLoggedInUser() override;
   const User* GetActiveUser() const override;
   User* GetActiveUser() override;
   const User* GetPrimaryUser() const override;
-  void SaveUserOAuthStatus(const std::string& user_id,
+  void SaveUserOAuthStatus(const UserID& user_id,
                            User::OAuthTokenStatus oauth_token_status) override;
-  void SaveForceOnlineSignin(const std::string& user_id,
+  void SaveForceOnlineSignin(const UserID& user_id,
                              bool force_online_signin) override;
-  void SaveUserDisplayName(const std::string& user_id,
+  void SaveUserDisplayName(const UserID& user_id,
                            const base::string16& display_name) override;
-  base::string16 GetUserDisplayName(const std::string& user_id) const override;
-  void SaveUserDisplayEmail(const std::string& user_id,
+  base::string16 GetUserDisplayName(const UserID& user_id) const override;
+  void SaveUserDisplayEmail(const UserID& user_id,
                             const std::string& display_email) override;
-  std::string GetUserDisplayEmail(const std::string& user_id) const override;
-  void SaveUserType(const std::string& user_id,
+  std::string GetUserDisplayEmail(const UserID& user_id) const override;
+  void SaveUserType(const UserID& user_id,
                     const UserType& user_type) override;
-  void UpdateUserAccountData(const std::string& user_id,
+  void UpdateUserAccountData(const UserID& user_id,
                              const UserAccountData& account_data) override;
   bool IsCurrentUserOwner() const override;
   bool IsCurrentUserNew() const override;
@@ -97,7 +97,7 @@ class USER_MANAGER_EXPORT UserManagerBase : public UserManager {
   bool IsLoggedInAsStub() const override;
   bool IsSessionStarted() const override;
   bool IsUserNonCryptohomeDataEphemeral(
-      const std::string& user_id) const override;
+      const UserID& user_id) const override;
   void AddObserver(UserManager::Observer* obs) override;
   void RemoveObserver(UserManager::Observer* obs) override;
   void AddSessionStateObserver(
@@ -131,20 +131,20 @@ class USER_MANAGER_EXPORT UserManagerBase : public UserManager {
                                const int in_value) override;
   void UpdateGaiaID(const UserID& user_id, const std::string& gaia_id) override;
   bool FindGaiaID(const UserID& user_id, std::string* out_value) override;
-  void UpdateUsingSAML(const std::string& user_id,
+  void UpdateUsingSAML(const UserID& user_id,
                        const bool using_saml) override;
-  bool FindUsingSAML(const std::string& user_id) override;
+  bool FindUsingSAML(const UserID& user_id) override;
   void SetKnownUserDeviceId(const UserID& user_id,
                             const std::string& device_id) override;
   std::string GetKnownUserDeviceId(const UserID& user_id) override;
-  void UpdateReauthReason(const std::string& user_id,
+  void UpdateReauthReason(const UserID& user_id,
                           const int reauth_reason) override;
-  bool FindReauthReason(const std::string& user_id, int* out_value) override;
+  bool FindReauthReason(const UserID& user_id, int* out_value) override;
 
   virtual void SetIsCurrentUserNew(bool is_new);
 
   // TODO(xiyuan): Figure out a better way to expose this info.
-  virtual bool HasPendingBootstrap(const std::string& user_id) const;
+  virtual bool HasPendingBootstrap(const UserID& user_id) const;
 
   // Helper function that copies users from |users_list| to |users_vector| and
   // |users_set|. Duplicates and users already present in |existing_users| are
@@ -182,7 +182,7 @@ class USER_MANAGER_EXPORT UserManagerBase : public UserManager {
 
   // Handle OAuth token |status| change for |user_id|.
   virtual void HandleUserOAuthTokenStatusChange(
-      const std::string& user_id,
+      const UserID& user_id,
       User::OAuthTokenStatus status) const = 0;
 
   // Returns true if device is enterprise managed.
@@ -219,36 +219,36 @@ class USER_MANAGER_EXPORT UserManagerBase : public UserManager {
 
   // Implementation for RemoveUser method. It is synchronous. It is called from
   // RemoveUserInternal after owner check.
-  virtual void RemoveNonOwnerUserInternal(const std::string& user_email,
+  virtual void RemoveNonOwnerUserInternal(const UserID& user_id,
                                           RemoveUserDelegate* delegate);
 
   // Removes a regular or supervised user from the user list.
   // Returns the user if found or NULL otherwise.
   // Also removes the user from the persistent user list.
-  User* RemoveRegularOrSupervisedUserFromList(const std::string& user_id);
+  User* RemoveRegularOrSupervisedUserFromList(const UserID& user_id);
 
   // Implementation for RemoveUser method. This is an asynchronous part of the
   // method, that verifies that owner will not get deleted, and calls
   // |RemoveNonOwnerUserInternal|.
-  virtual void RemoveUserInternal(const std::string& user_email,
+  virtual void RemoveUserInternal(const UserID& user_id,
                                   RemoveUserDelegate* delegate);
 
   // Removes data stored or cached outside the user's cryptohome (wallpaper,
   // avatar, OAuth token status, display name, display email).
-  virtual void RemoveNonCryptohomeData(const std::string& user_id);
+  virtual void RemoveNonCryptohomeData(const UserID& user_id);
 
   // Check for a particular user type.
 
   // Returns true if |user_id| represents demo app.
-  virtual bool IsDemoApp(const std::string& user_id) const = 0;
+  virtual bool IsDemoApp(const UserID& user_id) const = 0;
 
   // Returns true if |user_id| represents kiosk app.
-  virtual bool IsKioskApp(const std::string& user_id) const = 0;
+  virtual bool IsKioskApp(const UserID& user_id) const = 0;
 
   // Returns true if |user_id| represents public account that has been marked
   // for deletion.
   virtual bool IsPublicAccountMarkedForRemoval(
-      const std::string& user_id) const = 0;
+      const UserID& user_id) const = 0;
 
   // These methods are called when corresponding user type has signed in.
 
@@ -265,13 +265,13 @@ class USER_MANAGER_EXPORT UserManagerBase : public UserManager {
   virtual void PublicAccountUserLoggedIn(User* user) = 0;
 
   // Indicates that a regular user just logged in.
-  virtual void RegularUserLoggedIn(const std::string& user_id);
+  virtual void RegularUserLoggedIn(const UserID& user_id);
 
   // Indicates that a regular user just logged in as ephemeral.
-  virtual void RegularUserLoggedInAsEphemeral(const std::string& user_id);
+  virtual void RegularUserLoggedInAsEphemeral(const UserID& user_id);
 
   // Indicates that a supervised user just logged in.
-  virtual void SupervisedUserLoggedIn(const std::string& user_id) = 0;
+  virtual void SupervisedUserLoggedIn(const UserID& user_id) = 0;
 
   // Getters/setters for private members.
 
@@ -280,10 +280,10 @@ class USER_MANAGER_EXPORT UserManagerBase : public UserManager {
   virtual bool GetEphemeralUsersEnabled() const;
   virtual void SetEphemeralUsersEnabled(bool enabled);
 
-  virtual void SetOwnerEmail(std::string owner_user_id);
+  virtual void SetOwnerID(const UserID& owner_user_id);
 
-  virtual const std::string& GetPendingUserSwitchID() const;
-  virtual void SetPendingUserSwitchID(std::string user_id);
+  virtual const UserID& GetPendingUserSwitchID() const;
+  virtual void SetPendingUserSwitchID(const UserID& user_id);
 
   // The logged-in user that is currently active in current session.
   // NULL until a user has logged in, then points to one
@@ -320,21 +320,21 @@ class USER_MANAGER_EXPORT UserManagerBase : public UserManager {
 
   // Returns the user with the given email address if found in the persistent
   // list. Returns |NULL| otherwise.
-  const User* FindUserInList(const std::string& user_id) const;
+  const User* FindUserInList(const UserID& user_id) const;
 
   // Returns |true| if user with the given id is found in the persistent list.
   // Returns |false| otherwise. Does not trigger user loading.
-  bool UserExistsInList(const std::string& user_id) const;
+  bool UserExistsInList(const UserID& user_id) const;
 
   // Same as FindUserInList but returns non-const pointer to User object.
-  User* FindUserInListAndModify(const std::string& user_id);
+  User* FindUserInListAndModify(const UserID& user_id);
 
   // Reads user's oauth token status from local state preferences.
-  User::OAuthTokenStatus LoadUserOAuthStatus(const std::string& user_id) const;
+  User::OAuthTokenStatus LoadUserOAuthStatus(const UserID& user_id) const;
 
   // Read a flag indicating whether online authentication against GAIA should
   // be enforced during the user's next sign-in from local state preferences.
-  bool LoadForceOnlineSignin(const std::string& user_id) const;
+  bool LoadForceOnlineSignin(const UserID& user_id) const;
 
   // Notifies observers that merge session state had changed.
   void NotifyMergeSessionStateChanged();
@@ -352,14 +352,14 @@ class USER_MANAGER_EXPORT UserManagerBase : public UserManager {
   void SetLRUUser(User* user);
 
   // Sends metrics in response to a user with gaia account (regular) logging in.
-  void SendGaiaUserLoginMetrics(const std::string& user_id);
+  void SendGaiaUserLoginMetrics(const UserID& user_id);
 
   // Sets account locale for user with id |user_id|.
-  virtual void UpdateUserAccountLocale(const std::string& user_id,
+  virtual void UpdateUserAccountLocale(const UserID& user_id,
                                        const std::string& locale);
 
   // Updates user account after locale was resolved.
-  void DoUpdateAccountLocale(const std::string& user_id,
+  void DoUpdateAccountLocale(const UserID& user_id,
                              scoped_ptr<std::string> resolved_locale);
 
   // Removes all user preferences associated with |user_id|.
@@ -392,9 +392,9 @@ class USER_MANAGER_EXPORT UserManagerBase : public UserManager {
   // policy yet.
   bool ephemeral_users_enabled_;
 
-  // Cached name of device owner. Defaults to empty string if the value has not
+  // Cached id of device owner. Defaults to empty id if the value has not
   // been read from trusted device policy yet.
-  std::string owner_email_;
+  UserID owner_id_;
 
   ObserverList<UserManager::Observer> observer_list_;
 
@@ -407,12 +407,12 @@ class USER_MANAGER_EXPORT UserManagerBase : public UserManager {
 
   // ID of the user just added to the session that needs to be activated
   // as soon as user's profile is loaded.
-  std::string pending_user_switch_;
+  user_manager::UserID pending_user_switch_;
 
   // ID of the user that was active in the previous session.
   // Preference value is stored here before first user signs in
   // because pref will be overidden once session restore starts.
-  std::string last_session_active_user_;
+  user_manager::UserID last_session_active_user_;
   bool last_session_active_user_initialized_;
 
   // TaskRunner for UI thread.