Implement new invalidations ack tracking system

sync/notifier/invalidator_registrar_unittest.cc

Index: sync/notifier/invalidator_registrar_unittest.cc
diff --git a/sync/notifier/invalidator_registrar_unittest.cc b/sync/notifier/invalidator_registrar_unittest.cc
index 7a014010939b464ed8620f57413ead9f5ff5d990..c527bc5e0236080998f0a401b8a23ef964ae12dd 100644
--- a/sync/notifier/invalidator_registrar_unittest.cc
+++ b/sync/notifier/invalidator_registrar_unittest.cc
@@ -42,11 +42,6 @@ class RegistrarInvalidator : public Invalidator {
     registrar_.UnregisterHandler(handler);
   }
 
-  virtual void Acknowledge(const invalidation::ObjectId& id,
-                           const AckHandle& ack_handle) OVERRIDE {
-    // Do nothing.
-  }
-
   virtual InvalidatorState GetInvalidatorState() const OVERRIDE {
     return registrar_.GetInvalidatorState();
   }