[Sync] InvalidationService shouldn't CHECK when registering ObjectId for more than one handler

components/invalidation/p2p_invalidator.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.
 //
 // An invalidator that uses p2p invalidations based on XMPP push
 // notifications.  Used only for sync integration tests.
 
 #ifndef COMPONENTS_INVALIDATION_P2P_INVALIDATOR_H_
 #define COMPONENTS_INVALIDATION_P2P_INVALIDATOR_H_
 
@@ skipping 84 matching lines @@
   // to send notifications to all clients except for the one that triggered the
   // notification.  See crbug.com/97780.
   P2PInvalidator(scoped_ptr<notifier::PushClient> push_client,
                  const std::string& invalidator_client_id,
                  P2PNotificationTarget send_notification_target);
 
   ~P2PInvalidator() override;
 
   // Invalidator implementation.
   void RegisterHandler(InvalidationHandler* handler) override;
-  void UpdateRegisteredIds(InvalidationHandler* handler,
+  bool UpdateRegisteredIds(InvalidationHandler* handler,
                            const ObjectIdSet& ids) override;
   void UnregisterHandler(InvalidationHandler* handler) override;
   InvalidatorState GetInvalidatorState() const override;
   void UpdateCredentials(const std::string& email,
                          const std::string& token) override;
   void RequestDetailedStatus(base::Callback<void(const base::DictionaryValue&)>
                                  callback) const override;
 
   // PushClientObserver implementation.
   void OnNotificationsEnabled() override;
@@ skipping 23 matching lines @@
   bool notifications_enabled_;
   // Which set of clients should be sent notifications.
   P2PNotificationTarget send_notification_target_;
 
   DISALLOW_COPY_AND_ASSIGN(P2PInvalidator);
 };
 
 }  // namespace syncer
 
 #endif  // COMPONENTS_INVALIDATION_P2P_INVALIDATOR_H_