Implement support for disabling sync through configuration management.

chrome/browser/sync/profile_sync_service_observer.h

+// Copyright (c) 2010 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;
+ protected:
+  virtual ~ProfileSyncServiceObserver() { }
+};
+
+#endif  // CHROME_BROWSER_SYNC_PROFILE_SYNC_SERVICE_OBSERVER_H_