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

components/invalidation/invalidation_service.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 COMPONENTS_INVALIDATION_INVALIDATION_SERVICE_H_
 #define COMPONENTS_INVALIDATION_INVALIDATION_SERVICE_H_
 
 #include "base/callback_forward.h"
 #include "components/invalidation/invalidation_util.h"
 #include "components/invalidation/invalidator_state.h"
@@ skipping 58 matching lines @@
 
   // Starts sending notifications to |handler|.  |handler| must not be NULL,
   // and it must not already be registered.
   //
   // Handler registrations are persisted across restarts of sync.
   virtual void RegisterInvalidationHandler(
       syncer::InvalidationHandler* handler) = 0;
 
   // 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.
+  // at most one handler.  If ID is already registered function returns false.
   //
   // Registered IDs are persisted across restarts of sync.
-  virtual void UpdateRegisteredInvalidationIds(
+  virtual bool UpdateRegisteredInvalidationIds(
       syncer::InvalidationHandler* handler,
-      const syncer::ObjectIdSet& ids) = 0;
+      const syncer::ObjectIdSet& ids) WARN_UNUSED_RESULT = 0;
 
   // 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|.
   //
   // Handler registrations are persisted across restarts of sync.
   virtual void UnregisterInvalidationHandler(
       syncer::InvalidationHandler* handler) = 0;
 
   // Returns the current invalidator state.  When called from within
@@ skipping 12 matching lines @@
   virtual void RequestDetailedStatus(
       base::Callback<void(const base::DictionaryValue&)> post_caller) const = 0;
 
   // Returns the identity provider.
   virtual IdentityProvider* GetIdentityProvider() = 0;
 };
 
 }  // namespace invalidation
 
 #endif  // COMPONENTS_INVALIDATION_INVALIDATION_SERVICE_H_