It is time.

ui/aura/window_tracker.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_AURA_WINDOW_TRACKER_H_
-#define UI_AURA_WINDOW_TRACKER_H_
-
-#include <set>
-
-#include "base/basictypes.h"
-#include "base/compiler_specific.h"
-#include "ui/aura/aura_export.h"
-#include "ui/aura/window_observer.h"
-
-namespace aura {
-
-// This class keeps track of a set of windows. A Window is removed either
-// explicitly by Remove(), or implicitly when the window is destroyed.
-class AURA_EXPORT WindowTracker : public WindowObserver {
- public:
-  typedef std::set<Window*> Windows;
-
-  WindowTracker();
-  virtual ~WindowTracker();
-
-  // Returns the set of windows being observed.
-  const std::set<Window*>& windows() const { return windows_; }
-
-  // Adds |window| to the set of Windows being tracked.
-  void Add(Window* window);
-
-  // Removes |window| from the set of windows being tracked.
-  void Remove(Window* window);
-
-  // Returns true if |window| was previously added and has not been removed or
-  // deleted.
-  bool Contains(Window* window);
-
-  // WindowObserver overrides:
-  virtual void OnWindowDestroying(Window* window) override;
-
- private:
-  Windows windows_;
-
-  DISALLOW_COPY_AND_ASSIGN(WindowTracker);
-};
-
-}  // namespace aura
-
-#endif  // UI_AURA_WINDOW_TRACKER_H_