Add a SupervisedUserServiceObserver.

chrome/browser/supervised_user/supervised_user_service_observer.h

+// Copyright 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 CHROME_BROWSER_SUPERVISED_USER_SUPERVISED_USER_SERVICE_OBSERVER_H_
+#define CHROME_BROWSER_SUPERVISED_USER_SUPERVISED_USER_SERVICE_OBSERVER_H_
+
+class SupervisedUserServiceObserver {
+ public:
+  // Called whenever the URL filter is updated, e.g. a manual exception or a
+  // content pack is added, or the default fallback behavior is changed.
+  virtual void OnURLFilterChanged() {}
+
+ protected:
+  virtual ~SupervisedUserServiceObserver() {}
+};
+
+#endif  // CHROME_BROWSER_SUPERVISED_USER_SUPERVISED_USER_SERVICE_OBSERVER_H_