Modal window in user session not blocks user adding screen.

ash/wm/stacking_controller.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 "ash/wm/stacking_controller.h"
 
 #include "ash/root_window_controller.h"
 #include "ash/session_state_delegate.h"
 #include "ash/shell.h"
 #include "ash/shell_window_ids.h"
@@ skipping 111 matching lines @@
     aura::RootWindow* root,
     aura::Window* window) const {
   DCHECK(IsSystemModal(window));
 
   // If screen lock is not active and user session is active,
   // all modal windows are placed into the normal modal container.
   // In case of missing transient parent (it could happen for alerts from
   // background pages) assume that the window belongs to user session.
   SessionStateDelegate* session_state_delegate =
       Shell::GetInstance()->session_state_delegate();
-  if ((!session_state_delegate->IsScreenLocked() &&
-       session_state_delegate->IsActiveUserSessionStarted()) ||
+  if (!session_state_delegate->IsUserSessionBlocked() ||
       !window->transient_parent()) {
     return GetContainerById(root,
                             internal::kShellWindowId_SystemModalContainer);
   }
 
   // Otherwise those that originate from LockScreen container and above are
   // placed in the screen lock modal container.
   int window_container_id = window->transient_parent()->parent()->id();
   aura::Window* container = NULL;
   if (window_container_id < internal::kShellWindowId_LockScreenContainer) {
     container = GetContainerById(
         root, internal::kShellWindowId_SystemModalContainer);
   } else {
     container = GetContainerById(
         root, internal::kShellWindowId_LockSystemModalContainer);
   }
 
   return container;
 }
 
 }  // namespace ash