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

chrome/browser/app_controller_mac_browsertest.mm

Index: chrome/browser/app_controller_mac_browsertest.mm
diff --git a/chrome/browser/app_controller_mac_browsertest.mm b/chrome/browser/app_controller_mac_browsertest.mm
index 61400016edca21f617cb66d2f241155eaea5c767..ca65c24781ee05bdb9dd2717f5a3832d84ac9b34 100644
--- a/chrome/browser/app_controller_mac_browsertest.mm
+++ b/chrome/browser/app_controller_mac_browsertest.mm
@@ -134,12 +134,12 @@ void CreateProfileCallback(const base::Closure& quit_closure,
     quit_closure.Run();
 }
 
-void CreateAndWaitForGuestProfile() {
+void CreateAndWaitForProfileWithPath(const base::FilePath& path) {
   ProfileManager::CreateCallback create_callback =
       base::Bind(&CreateProfileCallback,
                  base::MessageLoop::current()->QuitClosure());
   g_browser_process->profile_manager()->CreateProfileAsync(
-      ProfileManager::GetGuestProfilePath(),
+      path,
       create_callback,
       base::string16(),
       base::string16(),
@@ -177,10 +177,10 @@ IN_PROC_BROWSER_TEST_F(AppControllerNewProfileManagementBrowserTest,
 // Test that for a locked last profile, a reopen event opens the User Manager.
 IN_PROC_BROWSER_TEST_F(AppControllerNewProfileManagementBrowserTest,
                        LockedProfileReopenWithNoWindows) {
-  // The User Manager uses the guest profile as its underlying profile. To
+  // The User Manager uses a special profile as its underlying profile. To
   // minimize flakiness due to the scheduling/descheduling of tasks on the
-  // different threads, pre-initialize the guest profile before it is needed.
-  CreateAndWaitForGuestProfile();
+  // different threads, pre-initialize this profile before it is needed.
+  CreateAndWaitForProfileWithPath(ProfileManager::GetUserManagerProfilePath());
   base::scoped_nsobject<AppController> ac([[AppController alloc] init]);
 
   // Lock the active profile.
@@ -206,7 +206,7 @@ IN_PROC_BROWSER_TEST_F(AppControllerNewProfileManagementBrowserTest,
                        GuestProfileReopenWithNoWindows) {
   // Create the guest profile, and set it as the last used profile so the
   // app controller can use it on init.
-  CreateAndWaitForGuestProfile();
+  CreateAndWaitForProfileWithPath(ProfileManager::GetGuestProfilePath());
   PrefService* local_state = g_browser_process->local_state();
   local_state->SetString(prefs::kProfileLastUsed, chrome::kGuestProfileDir);