WIP CallbackList in action

chrome/browser/user_style_sheet_watcher.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 CHROME_BROWSER_USER_STYLE_SHEET_WATCHER_H_
 #define CHROME_BROWSER_USER_STYLE_SHEET_WATCHER_H_
 
 #include "base/callback_forward.h"
 #include "base/files/file_path.h"
 #include "base/files/file_path_watcher.h"
@@ skipping 14 matching lines @@
     : public content::NotificationObserver,
       public RefcountedBrowserContextKeyedService {
  public:
   UserStyleSheetWatcher(Profile* profile, const base::FilePath& profile_path);
 
   void Init();
 
   GURL user_style_sheet() const;
 
   // Register a callback to be called whenever the stylesheet gets updated.
-  void RegisterOnStyleSheetUpdatedCallback(const base::Closure& callback);
+  base::Closure RegisterOnStyleSheetUpdatedCallback(
+      const base::Closure& callback);
 
   // content::NotificationObserver interface
   virtual void Observe(int type,
                        const content::NotificationSource& source,
                        const content::NotificationDetails& details) OVERRIDE;
 
   // RefCountedProfileKeyedBase method override.
   virtual void ShutdownOnUIThread() OVERRIDE;
 
  private:
@@ skipping 12 matching lines @@
 
   // Watches for changes to the css file so we can reload the style sheet.
   scoped_ptr<base::FilePathWatcher> file_watcher_;
 
   content::NotificationRegistrar registrar_;
 
   DISALLOW_COPY_AND_ASSIGN(UserStyleSheetWatcher);
 };
 
 #endif  // CHROME_BROWSER_USER_STYLE_SHEET_WATCHER_H_