It is time.

ui/views/widget/widget_removals_observer.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_WIDGET_WIDGET_REMOVALS_OBSERVER_H_
-#define UI_VIEWS_WIDGET_WIDGET_REMOVALS_OBSERVER_H_
-
-#include "ui/views/views_export.h"
-
-namespace views {
-
-class Widget;
-class View;
-
-// |WidgetRemovalsObserver| complements |WidgetObserver| with additional
-// notifications. These include events occurring during tear down like view
-// removal. For this reason, it is recommended that subclasses not also inherit
-// from |View|.
-class VIEWS_EXPORT WidgetRemovalsObserver {
- public:
-  // Called immediately before a descendant view of |widget| is removed.
-  virtual void OnWillRemoveView(Widget* widget, View* view) {}
-
- protected:
-  virtual ~WidgetRemovalsObserver() {}
-};
-
-}  // namespace views
-
-#endif  // UI_VIEWS_WIDGET_WIDGET_REMOVALS_OBSERVER_H_