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

chrome/browser/profiles/profile_manager.cc

Index: chrome/browser/profiles/profile_manager.cc
diff --git a/chrome/browser/profiles/profile_manager.cc b/chrome/browser/profiles/profile_manager.cc
index 0f2292dfed810a657571a2e7d6ba828939e9076c..b4df47d887fac0ed284bc38c6c4976a6c0708444 100644
--- a/chrome/browser/profiles/profile_manager.cc
+++ b/chrome/browser/profiles/profile_manager.cc
@@ -599,6 +599,16 @@ base::FilePath ProfileManager::GetGuestProfilePath() {
   return guest_path.Append(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.Append(chrome::kUserManagerProfileDir);
+}
+
 base::FilePath ProfileManager::GenerateNextProfileDirectoryPath() {
   PrefService* local_state = g_browser_process->local_state();
   DCHECK(local_state);
@@ -1120,7 +1130,9 @@ ProfileManager::ProfileInfo* ProfileManager::GetProfileInfoByPath(
 }
 
 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())