Update desktop tree when Aura windows are removed.

ui/views/accessibility/ax_window_obj_wrapper.h

 // Copyright 2014 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.
 
 #ifndef UI_VIEWS_ACCESSIBILITY_AX_WINDOW_OBJ_WRAPPER_H_
 #define UI_VIEWS_ACCESSIBILITY_AX_WINDOW_OBJ_WRAPPER_H_
 
 #include <stdint.h>
 
 #include "base/macros.h"
@@ skipping 20 matching lines @@
   void set_is_alert(bool is_alert) { is_alert_ = is_alert; }
 
   // AXAuraObjWrapper overrides.
   AXAuraObjWrapper* GetParent() override;
   void GetChildren(std::vector<AXAuraObjWrapper*>* out_children) override;
   void Serialize(ui::AXNodeData* out_node_data) override;
   int32_t GetID() override;
 
   // WindowObserver overrides.
   void OnWindowDestroyed(aura::Window* window) override;
+  void OnWindowDestroying(aura::Window* window) override;
+  void OnWindowHierarchyChanged(const HierarchyChangeParams& params) override;
 
  private:
   aura::Window* window_;
 
   bool is_alert_;
 
   DISALLOW_COPY_AND_ASSIGN(AXWindowObjWrapper);
 };
 
 }  // namespace views
 
 #endif  // UI_VIEWS_ACCESSIBILITY_AX_WINDOW_OBJ_WRAPPER_H_