Close mirroring window only when necessary

ash/shell.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/shell.h"
 
 #include <algorithm>
 #include <string>
 
 #include "ash/accelerators/accelerator_controller.h"
@@ skipping 740 matching lines @@
   window_cycle_controller_.reset();
   window_selector_controller_.reset();
   mru_window_tracker_.reset();
 
   // |shelf_window_watcher_| has a weak pointer to |shelf_Model_|
   // and has window observers.
   shelf_window_watcher_.reset();
 
   // Destroy all child windows including widgets.
   display_controller_->CloseChildWindows();
-  display_controller_->CloseMirroringDisplay();
 
   // Chrome implementation of shelf delegate depends on FocusClient,
   // so must be deleted before |focus_client_|.
   shelf_delegate_.reset();
   focus_client_.reset();
 
   // Destroy SystemTrayNotifier after destroying SystemTray as TrayItems
   // needs to remove observers from it.
   system_tray_notifier_.reset();
 
@@ skipping 405 matching lines @@
 ////////////////////////////////////////////////////////////////////////////////
 // Shell, aura::client::ActivationChangeObserver implementation:
 
 void Shell::OnWindowActivated(aura::Window* gained_active,
                               aura::Window* lost_active) {
   if (gained_active)
     target_root_window_ = gained_active->GetRootWindow();
 }
 
 }  // namespace ash