Implement Invalidator::Acknowledge

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 f833940c1713b34ad289533120e69e0e3f71bf18..fe4b409244bb04f2630d50a4ca80a7783a735226 100644
--- a/sync/notifier/invalidator_registrar_unittest.cc
+++ b/sync/notifier/invalidator_registrar_unittest.cc
@@ -43,6 +43,11 @@ 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();
   }