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diff --git a/sync/notifier/sync_notifier_registrar.h b/sync/notifier/sync_notifier_registrar.h
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+++ b/sync/notifier/sync_notifier_registrar.h
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+// 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 SYNC_NOTIFIER_SYNC_NOTIFIER_REGISTRAR_H_
+#define SYNC_NOTIFIER_SYNC_NOTIFIER_REGISTRAR_H_
+
+#include <map>
+
+#include "base/basictypes.h"
+#include "base/observer_list.h"
+#include "base/threading/thread_checker.h"
+#include "sync/notifier/invalidation_util.h"
+#include "sync/notifier/object_id_payload_map.h"
+#include "sync/notifier/sync_notifier_observer.h"
+
+namespace invalidation {
+class ObjectId;
+}  // namespace invalidation
+
+namespace syncer {
+
+// A helper class for implementations of the SyncNotifier interface.  It helps
+// keep track of registered handlers and which object ID registrations are
+// associated with which handlers, so implementors can just reuse the logic
+// here to dispatch invalidations and other interesting notifications.
+class SyncNotifierRegistrar {
+ public:
+  SyncNotifierRegistrar();
+  ~SyncNotifierRegistrar();
+
+  // Starts sending notifications to |handler|.  |handler| must not be NULL,
+  // and it must already be registered.
+  void RegisterHandler(SyncNotifierObserver* handler);
+
+
+  // Updates the set of ObjectIds associated with |handler|.  |handler| must
+  // not be NULL, and must already be registered.  An ID must be registered for
+  // at most one handler.
+  void UpdateRegisteredIds(SyncNotifierObserver* handler,
+                           const ObjectIdSet& ids);
+
+  // Stops sending notifications to |handler|.  |handler| must not be NULL, and
+  // it must already be registered.  Note that this doesn't unregister the IDs
+  // associated with |handler|.
+  void UnregisterHandler(SyncNotifierObserver* handler);
+
+  // Returns the set of all IDs that are registered to some handler (even
+  // handlers that have been unregistered).
+  ObjectIdSet GetAllRegisteredIds() const;
+
+  // Sorts incoming invalidations into a bucket for each handler and then
+  // dispatches the batched invalidations to the corresponding handler.
+  // Invalidations for IDs with no corresponding handler are dropped, as are
+  // invalidations for handlers that are not added.
+  void DispatchInvalidationsToHandlers(const ObjectIdPayloadMap& id_payloads,
+                                       IncomingNotificationSource source);
+
+  // Calls the given handler method for each handler that has registered IDs.
+  void EmitOnNotificationsEnabled();
+  void EmitOnNotificationsDisabled(NotificationsDisabledReason reason);
+
+  // Needed for death tests.
+  void DetachFromThreadForTest();
+
+ private:
+  typedef std::map<invalidation::ObjectId, SyncNotifierObserver*,
+                   ObjectIdLessThan>
+      IdHandlerMap;
+
+  SyncNotifierObserver* ObjectIdToHandler(const invalidation::ObjectId& id);
+
+  base::ThreadChecker thread_checker_;
+  ObserverList<SyncNotifierObserver> handlers_;
+  IdHandlerMap id_to_handler_map_;
+
+  DISALLOW_COPY_AND_ASSIGN(SyncNotifierRegistrar);
+};
+
+}  // namespace syncer
+
+#endif  // SYNC_NOTIFIER_SYNC_NOTIFIER_REGISTRAR_H_