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

chrome/browser/profiles/profile_manager.cc

 // 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.
 
 #include "chrome/browser/profiles/profile_manager.h"
 
 #include <set>
 
 #include "base/bind.h"
 #include "base/command_line.h"
@@ skipping 578 matching lines @@
   return new_path;
 }
 
 // static
 base::FilePath ProfileManager::GetGuestProfilePath() {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
 
   ProfileManager* profile_manager = g_browser_process->profile_manager();
 
   base::FilePath guest_path = profile_manager->user_data_dir();
-  return guest_path.Append(chrome::kGuestProfileDir);
+  return guest_path.AppendASCII(chrome::kGuestProfileDir);
+}
+
+// static
+base::FilePath ProfileManager::GetUserManagerProfilePath() {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
+
+  ProfileManager* profile_manager = g_browser_process->profile_manager();
+
+  base::FilePath profile_path = profile_manager->user_data_dir();
+  return profile_path.AppendASCII(chrome::kUserManagerProfileDir);
 }
 
 base::FilePath ProfileManager::GenerateNextProfileDirectoryPath() {
   PrefService* local_state = g_browser_process->local_state();
   DCHECK(local_state);
 
   DCHECK(profiles::IsMultipleProfilesEnabled());
 
   // Create the next profile in the next available directory slot.
   int next_directory = local_state->GetInteger(prefs::kProfilesNumCreated);
@@ skipping 503 matching lines @@
   return info;
 }
 
 ProfileManager::ProfileInfo* ProfileManager::GetProfileInfoByPath(
     const base::FilePath& path) const {
   ProfilesInfoMap::const_iterator iter = profiles_info_.find(path);
   return (iter == profiles_info_.end()) ? NULL : iter->second.get();
 }
 
 void ProfileManager::AddProfileToCache(Profile* profile) {
-  if (profile->IsGuestSession())
+  // Don't add guest profiles or the generic user manager profile to the cache.
+  if (profile->IsGuestSession() ||
+      profile->GetPath() == ProfileManager::GetUserManagerProfilePath())
     return;
   ProfileInfoCache& cache = GetProfileInfoCache();
   if (profile->GetPath().DirName() != cache.GetUserDataDir())
     return;
 
   if (cache.GetIndexOfProfileWithPath(profile->GetPath()) != std::string::npos)
     return;
 
   base::string16 username = base::UTF8ToUTF16(profile->GetPrefs()->GetString(
       prefs::kGoogleServicesUsername));
@@ skipping 152 matching lines @@
           last_non_managed_profile_path.BaseName().MaybeAsASCII());
       FinishDeletingProfile(profile_to_delete_path);
     }
   }
 }
 #endif
 
 ProfileManagerWithoutInit::ProfileManagerWithoutInit(
     const base::FilePath& user_data_dir) : ProfileManager(user_data_dir) {
 }