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

chrome/browser/profiles/profile_info_cache.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_PROFILES_PROFILE_INFO_CACHE_H_
 #define CHROME_BROWSER_PROFILES_PROFILE_INFO_CACHE_H_
 
 #include <map>
 #include <string>
 #include <vector>
 
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
 #include "base/files/file_path.h"
 #include "base/memory/weak_ptr.h"
 #include "base/observer_list.h"
 #include "base/strings/string16.h"
 #include "chrome/browser/profiles/profile_info_cache_observer.h"
 #include "chrome/browser/profiles/profile_info_interface.h"
 
 namespace gfx {
 class Image;
 }
 
 namespace base {
 class DictionaryValue;
 }
 
+namespace user_manager {
+class UserID;
+}
+
 class PrefService;
 class PrefRegistrySimple;
 class ProfileAvatarDownloader;
 
 // This class saves various information about profiles to local preferences.
 // This cache can be used to display a list of profiles without having to
 // actually load the profiles from disk.
 class ProfileInfoCache : public ProfileInfoInterface,
                          public base::SupportsWeakPtr<ProfileInfoCache> {
  public:
   ProfileInfoCache(PrefService* prefs, const base::FilePath& user_data_dir);
   ~ProfileInfoCache() override;
 
   // If the |supervised_user_id| is non-empty, the profile will be marked to be
   // omitted from the avatar-menu list on desktop versions. This is used while a
   // supervised user is in the process of being registered with the server. Use
   // SetIsOmittedProfileAtIndex() to clear the flag when the profile is ready to
   // be shown in the menu.
   void AddProfileToCache(const base::FilePath& profile_path,
                          const base::string16& name,
                          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:
   size_t GetNumberOfProfiles() const override;
   // Don't cache this value and reuse, because resorting the menu could cause
   // the item being referred to to change out from under you.
   size_t GetIndexOfProfileWithPath(
       const base::FilePath& profile_path) const override;
   base::string16 GetNameOfProfileAtIndex(size_t index) const override;
   base::string16 GetShortcutNameOfProfileAtIndex(size_t index) const override;
@@ skipping 13 matching lines @@
   // Returns the GAIA picture for the given profile. This may return NULL
   // if the profile does not have a GAIA picture or if the picture must be
   // loaded from disk.
   const gfx::Image* GetGAIAPictureOfProfileAtIndex(size_t index) const override;
   bool IsUsingGAIAPictureOfProfileAtIndex(size_t index) const override;
   bool ProfileIsSupervisedAtIndex(size_t index) const override;
   bool ProfileIsChildAtIndex(size_t index) const override;
   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;
   bool ProfileIsUsingDefaultAvatarAtIndex(size_t index) const override;
   bool ProfileIsAuthErrorAtIndex(size_t index) const;
 
   size_t GetAvatarIconIndexOfProfileAtIndex(size_t index) const;
 
   void SetProfileActiveTimeAtIndex(size_t index);
   // Warning: This will re-sort profiles and thus may change indices!
   void SetNameOfProfileAtIndex(size_t index, const base::string16& name);
   void SetShortcutNameOfProfileAtIndex(size_t index,
                                        const base::string16& name);
   void SetAuthInfoOfProfileAtIndex(size_t index,
                                    const std::string& gaia_id,
                                    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,
                                            bool running_background_apps);
   // Warning: This will re-sort profiles and thus may change indices!
   void SetGAIANameOfProfileAtIndex(size_t index, const base::string16& name);
   // Warning: This will re-sort profiles and thus may change indices!
   void SetGAIAGivenNameOfProfileAtIndex(size_t index,
                                         const base::string16& name);
   void SetGAIAPictureOfProfileAtIndex(size_t index, const gfx::Image* image);
@@ skipping 120 matching lines @@
       avatar_images_downloads_in_progress_;
 
   // Determines of the ProfileAvatarDownloader should be created and executed
   // or not. Only set to true for tests.
   bool disable_avatar_download_for_testing_;
 
   DISALLOW_COPY_AND_ASSIGN(ProfileInfoCache);
 };
 
 #endif  // CHROME_BROWSER_PROFILES_PROFILE_INFO_CACHE_H_