Implement Invalidator::Acknowledge

sync/notifier/p2p_invalidator.cc

Index: sync/notifier/p2p_invalidator.cc
diff --git a/sync/notifier/p2p_invalidator.cc b/sync/notifier/p2p_invalidator.cc
index 58943916712c0ba262b87dc31b9b14ffb77601e1..e71d1e3c0802a7dd897c3e460dae522dc65112c8 100644
--- a/sync/notifier/p2p_invalidator.cc
+++ b/sync/notifier/p2p_invalidator.cc
@@ -178,6 +178,12 @@ void P2PInvalidator::UnregisterHandler(InvalidationHandler* handler) {
   registrar_.UnregisterHandler(handler);
 }
 
+void P2PInvalidator::Acknowledge(const invalidation::ObjectId& id,
+                                 const AckHandle& ack_handle) {
+  DCHECK(thread_checker_.CalledOnValidThread());
+  // Do nothing for the P2P implementation.
+}
+
 InvalidatorState P2PInvalidator::GetInvalidatorState() const {
   DCHECK(thread_checker_.CalledOnValidThread());
   return registrar_.GetInvalidatorState();