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

chrome/browser/profiles/profile_info_cache.h

Index: chrome/browser/profiles/profile_info_cache.h
diff --git a/chrome/browser/profiles/profile_info_cache.h b/chrome/browser/profiles/profile_info_cache.h
index e090abd966bb7bdf0653659ecff08552caf8fadd..15c828f9e3fb1a8a41e34557beb02bbbc1edad88 100644
--- a/chrome/browser/profiles/profile_info_cache.h
+++ b/chrome/browser/profiles/profile_info_cache.h
@@ -26,6 +26,10 @@ namespace base {
 class DictionaryValue;
 }
 
+namespace user_manager {
+class UserID;
+}
+
 class PrefService;
 class PrefRegistrySimple;
 class ProfileAvatarDownloader;
@@ -49,7 +53,7 @@ class ProfileInfoCache : public ProfileInfoInterface,
                          const std::string& gaia_id,
                          const base::string16& user_name,
                          size_t icon_index,
-                         const std::string& supervised_user_id);
+                         const user_manager::UserID& supervised_user_id);
   void DeleteProfileFromCache(const base::FilePath& profile_path);
 
   // ProfileInfoInterface:
@@ -83,7 +87,7 @@ class ProfileInfoCache : public ProfileInfoInterface,
   bool ProfileIsLegacySupervisedAtIndex(size_t index) const override;
   bool IsOmittedProfileAtIndex(size_t index) const override;
   bool ProfileIsSigninRequiredAtIndex(size_t index) const override;
-  std::string GetSupervisedUserIdOfProfileAtIndex(size_t index) const override;
+  user_manager::UserID GetSupervisedUserIdOfProfileAtIndex(size_t index) const override;
   bool ProfileIsEphemeralAtIndex(size_t index) const override;
   bool ProfileIsUsingDefaultNameAtIndex(size_t index) const override;
   bool ProfileIsAuthenticatedAtIndex(size_t index) const override;
@@ -102,7 +106,7 @@ class ProfileInfoCache : public ProfileInfoInterface,
                                    const base::string16& user_name);
   void SetAvatarIconOfProfileAtIndex(size_t index, size_t icon_index);
   void SetIsOmittedProfileAtIndex(size_t index, bool is_omitted);
-  void SetSupervisedUserIdOfProfileAtIndex(size_t index, const std::string& id);
+  void SetSupervisedUserIdOfProfileAtIndex(size_t index, const user_manager::UserID& id);
   void SetLocalAuthCredentialsOfProfileAtIndex(size_t index,
                                                const std::string& auth);
   void SetBackgroundStatusOfProfileAtIndex(size_t index,