It is time.

ui/aura/window_tree_host_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_AURA_WINDOW_TREE_HOST_OBSERVER_H_
-#define UI_AURA_WINDOW_TREE_HOST_OBSERVER_H_
-
-#include "ui/aura/aura_export.h"
-
-namespace gfx {
-class Point;
-}
-
-namespace aura {
-class Window;
-class WindowTreeHost;
-
-class AURA_EXPORT WindowTreeHostObserver {
- public:
-  // Called when the host's client size has changed.
-  virtual void OnHostResized(const WindowTreeHost* host) {}
-
-  // Called when the host is moved on screen.
-  virtual void OnHostMoved(const WindowTreeHost* host,
-                           const gfx::Point& new_origin) {}
-
-  // Called when the native window system sends the host request to close.
-  virtual void OnHostCloseRequested(const WindowTreeHost* host) {}
-
- protected:
-  virtual ~WindowTreeHostObserver() {}
-};
-
-}  // namespace aura
-
-#endif  // UI_AURA_WINDOW_TREE_HOST_OBSERVER_H_