It is time.

ui/native_theme/native_theme_observer.h

-// Copyright (c) 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_NATIVE_THEME_NATIVE_THEME_OBSERVER_H_
-#define UI_NATIVE_THEME_NATIVE_THEME_OBSERVER_H_
-
-#include "ui/native_theme/native_theme_export.h"
-
-namespace ui {
-
-class NativeTheme;
-
-// Observers which are notified when the native theme changes.
-class NATIVE_THEME_EXPORT NativeThemeObserver {
- public:
-  // Called when the native theme changes. The observed theme is passed so that
-  // observers may handle changes to their associated native theme instances.
-  virtual void OnNativeThemeUpdated(ui::NativeTheme* observed_theme) = 0;
-
- protected:
-  virtual ~NativeThemeObserver();
-};
-
-}  // namespace ui
-
-#endif  // UI_NATIVE_THEME_NATIVE_THEME_OBSERVER_H_