Update Windows UI on system color changes.

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_