It is time.

ui/views/widget/widget_observer.h

-// 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.
-
-#ifndef UI_VIEWS_WIDGET_WIDGET_OBSERVER_H_
-#define UI_VIEWS_WIDGET_WIDGET_OBSERVER_H_
-
-#include "ui/views/views_export.h"
-
-namespace gfx {
-class Rect;
-}
-
-namespace views {
-
-class Widget;
-class View;
-
-// Observers can listen to various events on the Widgets.
-class VIEWS_EXPORT WidgetObserver {
- public:
-  // The closing notification is sent immediately in response to (i.e. in the
-  // same call stack as) a request to close the Widget (via Close() or
-  // CloseNow()).
-  virtual void OnWidgetClosing(Widget* widget) {}
-
-  // Invoked after notification is received from the event loop that the native
-  // widget has been created.
-  virtual void OnWidgetCreated(Widget* widget) {}
-
-  // The destroying event occurs immediately before the widget is destroyed.
-  // This typically occurs asynchronously with respect the the close request, as
-  // a result of a later invocation from the event loop.
-  virtual void OnWidgetDestroying(Widget* widget) {}
-
-  // Invoked after notification is received from the event loop that the native
-  // widget has been destroyed.
-  virtual void OnWidgetDestroyed(Widget* widget) {}
-
-  virtual void OnWidgetVisibilityChanging(Widget* widget, bool visible) {}
-
-  virtual void OnWidgetVisibilityChanged(Widget* widget, bool visible) {}
-
-  virtual void OnWidgetActivationChanged(Widget* widget, bool active) {}
-
-  virtual void OnWidgetBoundsChanged(Widget* widget,
-                                     const gfx::Rect& new_bounds) {}
-
- protected:
-  virtual ~WidgetObserver() {}
-};
-
-}  // namespace views
-
-#endif  // UI_VIEWS_WIDGET_WIDGET_OBSERVER_H_