Make use of InvalidationService

chrome/browser/sync/profile_sync_service_observer.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_SYNC_PROFILE_SYNC_SERVICE_OBSERVER_H_
 #define CHROME_BROWSER_SYNC_PROFILE_SYNC_SERVICE_OBSERVER_H_
 
 // Various UI components such as the New Tab page can be driven by observing
 // the ProfileSyncService through this interface.
 class ProfileSyncServiceObserver {
  public:
   // When one of the following events occurs, OnStateChanged() is called.
   // Observers should query the service to determine what happened.
   // - We initialized successfully.
   // - There was an authentication error and the user needs to reauthenticate.
   // - The sync servers are unavailable at this time.
   // - Credentials are now in flight for authentication.
   virtual void OnStateChanged() = 0;
+
+  // If a client wishes to handle sync cycle completed events in a special way,
+  // they can use this function.  By default, it re-routes to OnStateChanged().
+  virtual void OnSyncCycleCompleted();
  protected:
   virtual ~ProfileSyncServiceObserver() { }
 };
 
 #endif  // CHROME_BROWSER_SYNC_PROFILE_SYNC_SERVICE_OBSERVER_H_