Close mirroring window only when necessary

ash/display/display_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/display/display_controller.h"
 
 #include <algorithm>
 #include <cmath>
 #include <map>
 
@@ skipping 787 matching lines @@
     const DisplayInfoList& info_list) {
   if (GetDisplayManager()->IsInMirrorMode() ||
       GetDisplayManager()->IsInUnifiedMode()) {
     mirror_window_controller_->UpdateWindow(info_list);
     cursor_window_controller_->UpdateContainer();
   } else {
     NOTREACHED();
   }
 }
 
-void DisplayController::CloseMirroringDisplay() {
-  mirror_window_controller_->Close();
+void DisplayController::CloseMirroringDisplayIfNotNecessary() {
+  mirror_window_controller_->CloseIfNotNecessary();
   // If cursor_compositing is enabled for large cursor, the cursor window is
   // always on the desktop display (the visible cursor on the non-desktop
   // display is drawn through compositor mirroring). Therefore, it's unnecessary
   // to handle the cursor_window at all. See: http://crbug.com/412910
   if (!cursor_window_controller_->is_cursor_compositing_enabled())
     cursor_window_controller_->UpdateContainer();
 }
 
 void DisplayController::PreDisplayConfigurationChange(bool clear_focus) {
   FOR_EACH_OBSERVER(Observer, observers_, OnDisplayConfigurationChanging());
@@ skipping 82 matching lines @@
   Shell::GetInstance()->display_configurator_animation()
       ->StartFadeInAnimation();
 #endif
 }
 
 void DisplayController::SetMirrorModeAfterAnimation(bool mirror) {
   GetDisplayManager()->SetMirrorMode(mirror);
 }
 
 }  // namespace ash