Update Windows UI on system color changes.

ui/native_theme/native_theme.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_NATIVE_THEME_NATIVE_THEME_H_
 #define UI_NATIVE_THEME_NATIVE_THEME_H_
 
+#include "base/observer_list.h"
 #include "third_party/skia/include/core/SkColor.h"
 #include "ui/gfx/native_widget_types.h"
 #include "ui/native_theme/native_theme_export.h"
 
 class SkCanvas;
 
 namespace gfx {
 class Rect;
 class Size;
 }
 
 namespace ui {
 
+// Observers which are notified when the native theme changes.
+class NATIVE_THEME_EXPORT NativeThemeObserver {
+ public:
+  virtual ~NativeThemeObserver();
+
+  // Called whenever the underlying platform's native theme changes.
+  virtual void OnNativeThemeUpdate() = 0;
+};
+
 // This class supports drawing UI controls (like buttons, text fields, lists,
 // comboboxes, etc) that look like the native UI controls of the underlying
 // platform, such as Windows or Linux. It also supplies default colors for
 // dialog box backgrounds, etc., which are obtained from the system theme where
 // possible.
 //
 // The supported control types are listed in the Part enum.  These parts can be
 // in any state given by the State enum, where the actual definition of the
 // state is part-specific. The supported colors are listed in the ColorId enum.
 //
@@ skipping 272 matching lines @@
   // Return a color from the system theme.
   virtual SkColor GetSystemColor(ColorId color_id) const = 0;
 
   // Returns a shared instance of the native theme.
   // The returned object should not be deleted by the caller.  This function
   // is not thread safe and should only be called from the UI thread.
   // Each port of NativeTheme should provide its own implementation of this
   // function, returning the port's subclass.
   static NativeTheme* instance();
 
+  // Add or remove observers to be notified when the native theme changes.
+  void AddObserver(NativeThemeObserver* observer);
+  void RemoveObserver(NativeThemeObserver* observer);
+
  protected:
+  // Notify observers of native theme state changes.
+  void NotifyObservers();
+
   NativeTheme();
   virtual ~NativeTheme();
 
   unsigned int thumb_inactive_color_;
   unsigned int thumb_active_color_;
   unsigned int track_color_;
 
+ private:
+  // Observers to notify when the theme state changes.
+  ObserverList<NativeThemeObserver> native_theme_observers_;
+
   DISALLOW_COPY_AND_ASSIGN(NativeTheme);
 };
 
 }  // namespace ui
 
 #endif  // UI_NATIVE_THEME_NATIVE_THEME_H_