Implement Invalidator::Acknowledge

sync/notifier/fake_invalidator.cc

Index: sync/notifier/fake_invalidator.cc
diff --git a/sync/notifier/fake_invalidator.cc b/sync/notifier/fake_invalidator.cc
index b7cfd4dd4fcba1c5525d3d1626cc47f0be8e2435..c8216af75e952fe772924e43809ecea1c652f2f8 100644
--- a/sync/notifier/fake_invalidator.cc
+++ b/sync/notifier/fake_invalidator.cc
@@ -50,7 +50,7 @@ void FakeInvalidator::RegisterHandler(InvalidationHandler* handler) {
 }
 
 void FakeInvalidator::UpdateRegisteredIds(InvalidationHandler* handler,
-                                           const ObjectIdSet& ids) {
+                                          const ObjectIdSet& ids) {
   registrar_.UpdateRegisteredIds(handler, ids);
 }
 
@@ -58,6 +58,11 @@ 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();
 }