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

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

Index: chrome/browser/chromeos/login/users/supervised_user_manager.h
diff --git a/chrome/browser/chromeos/login/users/supervised_user_manager.h b/chrome/browser/chromeos/login/users/supervised_user_manager.h
index 82a4b0c5a474c31ac61a947f85a29be5f3ed6717..4bb0b63c2dedafea17ef4e116a6f8ca9c3183e38 100644
--- a/chrome/browser/chromeos/login/users/supervised_user_manager.h
+++ b/chrome/browser/chromeos/login/users/supervised_user_manager.h
@@ -17,6 +17,7 @@ class PrefRegistrySimple;
 
 namespace user_manager {
 class User;
+class UserID;
 }
 
 namespace chromeos {
@@ -55,7 +56,7 @@ class SupervisedUserManager {
 
   // Checks if given user have supervised users on this device.
 
-  virtual bool HasSupervisedUsers(const std::string& manager_id) const = 0;
+  virtual bool HasSupervisedUsers(const user_manager::UserID& manager_id) const = 0;
 
   // Creates supervised user with given |display_name| and |local_user_id|
   // and persists that to user list. Also links this user identified by
@@ -64,13 +65,13 @@ class SupervisedUserManager {
   // was a supervised user with such display name.
   // TODO(antrim): Refactor into a single struct to have only 1 getter.
   virtual const user_manager::User* CreateUserRecord(
-      const std::string& manager_id,
-      const std::string& local_user_id,
+      const user_manager::UserID& manager_id,
+      const user_manager::UserID& local_user_id,
       const std::string& sync_user_id,
       const base::string16& display_name) = 0;
 
   // Generates unique user ID for supervised user.
-  virtual std::string GenerateUserId() = 0;
+  virtual user_manager::UserID GenerateUserId() = 0;
 
   // Returns the supervised user with the given |display_name| if found in
   // the persistent list. Returns |NULL| otherwise.
@@ -84,30 +85,30 @@ class SupervisedUserManager {
 
   // Returns sync_user_id for supervised user with |user_id| or empty string if
   // such user is not found or it doesn't have user_id defined.
-  virtual std::string GetUserSyncId(const std::string& user_id) const = 0;
+  virtual std::string GetUserSyncId(const user_manager::UserID& user_id) const = 0;
 
   // Returns the display name for manager of user |user_id| if it is known
   // (was previously set by a |SaveUserDisplayName| call).
   // Otherwise, returns a manager id.
   virtual base::string16 GetManagerDisplayName(
-      const std::string& user_id) const = 0;
+      const user_manager::UserID& user_id) const = 0;
 
   // Returns the user id for manager of user |user_id| if it is known (user is
   // actually a managed user).
   // Otherwise, returns an empty string.
-  virtual std::string GetManagerUserId(const std::string& user_id) const = 0;
+  virtual user_manager::UserID GetManagerUserId(const user_manager::UserID& user_id) const = 0;
 
   // Returns the display email for manager of user |user_id| if it is known
   // (user is actually a managed user).
   // Otherwise, returns an empty string.
-  virtual std::string GetManagerDisplayEmail(const std::string& user_id)
+  virtual std::string GetManagerDisplayEmail(const user_manager::UserID& user_id)
       const = 0;
 
   // Create a record about starting supervised user creation transaction.
   virtual void StartCreationTransaction(const base::string16& display_name) = 0;
 
   // Add user id to supervised user creation transaction record.
-  virtual void SetCreationTransactionUserId(const std::string& user_id) = 0;
+  virtual void SetCreationTransactionUserId(const user_manager::UserID& user_id) = 0;
 
   // Remove supervised user creation transaction record.
   virtual void CommitCreationTransaction() = 0;
@@ -117,13 +118,13 @@ class SupervisedUserManager {
 
   // Fill |result| with public password-specific data for |user_id| from Local
   // State.
-  virtual void GetPasswordInformation(const std::string& user_id,
+  virtual void GetPasswordInformation(const user_manager::UserID& user_id,
                                       base::DictionaryValue* result) = 0;
 
   // Stores public password-specific data from |password_info| for |user_id| in
   // Local State.
   virtual void SetPasswordInformation(
-      const std::string& user_id,
+      const user_manager::UserID& user_id,
       const base::DictionaryValue* password_info) = 0;
 
   // Loads a sync oauth token in background, and passes it to callback.