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

chrome/browser/profiles/profile_manager.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.
 
 // This class keeps track of the currently-active profiles in the runtime.
 
 #ifndef CHROME_BROWSER_PROFILES_PROFILE_MANAGER_H_
 #define CHROME_BROWSER_PROFILES_PROFILE_MANAGER_H_
 
 #include <list>
@@ skipping 121 matching lines @@
   // asynchronously.
   static base::FilePath CreateMultiProfileAsync(
       const base::string16& name,
       const base::string16& icon_url,
       const CreateCallback& callback,
       const std::string& managed_user_id);
 
   // Returns the full path to be used for guest profiles.
   static base::FilePath GetGuestProfilePath();
 
+  // Returns the full path to be used by the user manager profile.
+  static base::FilePath GetUserManagerProfilePath();
+
   // Get the path of the next profile directory and increment the internal
   // count.
   // Lack of side effects:
   // This function doesn't actually create the directory or touch the file
   // system.
   base::FilePath GenerateNextProfileDirectoryPath();
 
   // Returns a ProfileInfoCache object which can be used to get information
   // about profiles without having to load them from disk.
   ProfileInfoCache& GetProfileInfoCache();
@@ skipping 198 matching lines @@
 class ProfileManagerWithoutInit : public ProfileManager {
  public:
   explicit ProfileManagerWithoutInit(const base::FilePath& user_data_dir);
 
  protected:
   virtual void DoFinalInitForServices(Profile*, bool) OVERRIDE {}
   virtual void DoFinalInitLogging(Profile*) OVERRIDE {}
 };
 
 #endif  // CHROME_BROWSER_PROFILES_PROFILE_MANAGER_H_