Implement new invalidations ack tracking system

sync/notifier/fake_invalidator.cc

 // 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.
 
 #include "sync/notifier/fake_invalidator.h"
 
 namespace syncer {
 
 FakeInvalidator::FakeInvalidator() {}
 
@@ skipping 31 matching lines @@
 
 void FakeInvalidator::UpdateRegisteredIds(InvalidationHandler* handler,
                                           const ObjectIdSet& ids) {
   registrar_.UpdateRegisteredIds(handler, ids);
 }
 
 void FakeInvalidator::UnregisterHandler(InvalidationHandler* handler) {
   registrar_.UnregisterHandler(handler);
 }
 
-void FakeInvalidator::Acknowledge(const invalidation::ObjectId& id,
-                                  const AckHandle& ack_handle) {
-  // Do nothing.
-}
-
 InvalidatorState FakeInvalidator::GetInvalidatorState() const {
   return registrar_.GetInvalidatorState();
 }
 
 void FakeInvalidator::UpdateCredentials(
     const std::string& email, const std::string& token) {
   email_ = email;
   token_ = token;
 }
 
 }  // namespace syncer