Implement Invalidator::Acknowledge

chrome/browser/sync/invalidation_frontend.h

Index: chrome/browser/sync/invalidation_frontend.h
diff --git a/chrome/browser/sync/invalidation_frontend.h b/chrome/browser/sync/invalidation_frontend.h
index 6f19b73c0dbd48937b52e018e2d98fdbaa91790c..0c767704f0b12fe0be6ad988e2f41a712aab6e27 100644
--- a/chrome/browser/sync/invalidation_frontend.h
+++ b/chrome/browser/sync/invalidation_frontend.h
@@ -82,6 +82,11 @@ class InvalidationFrontend {
   virtual void UnregisterInvalidationHandler(
       syncer::InvalidationHandler* handler) = 0;
 
+  // Sends an acknowledgement that an invalidation for |id| was successfully
+  // handled.
+  virtual void AcknowledgeInvalidation(const invalidation::ObjectId& id,
+                                       const syncer::AckHandle& ack_handle) = 0;
+
   // Returns the current invalidator state.  When called from within
   // InvalidationHandler::OnInvalidatorStateChange(), this must return
   // the updated state.