The User Manager should be backed by a special profile, not the guest one.

chrome/browser/profiles/profile_window.h

Index: chrome/browser/profiles/profile_window.h
diff --git a/chrome/browser/profiles/profile_window.h b/chrome/browser/profiles/profile_window.h
index aa224b6e75caa874cdd0768f27f15dd4f87d7714..0808bbe200adeef2d83d073982aab94ce2c6fb48 100644
--- a/chrome/browser/profiles/profile_window.h
+++ b/chrome/browser/profiles/profile_window.h
@@ -66,13 +66,13 @@ void CloseGuestProfileWindows();
 // Closes all the browser windows for |profile| and opens the user manager.
 void LockProfile(Profile* profile);
 
-// Creates or reuses the guest profile needed by the user manager. Based on
+// Creates or reuses the profile needed by the user manager. Based on
 // the value of |tutorial_mode|, the user manager can show a specific
 // tutorial, or no tutorial at all. If a tutorial is not shown, then
 // |profile_path_to_focus| could be used to specify which user should be
 // focused. |callback| is run with the custom url to be displayed, as well as
 // a pointer to the guest profile.
-void CreateGuestProfileForUserManager(
+void CreateUserManagerProfile(
     const base::FilePath& profile_path_to_focus,
     profiles::UserManagerTutorialMode tutorial_mode,
     const base::Callback<void(Profile*, const std::string&)>& callback);