Implement Invalidator::Acknowledge

chrome/browser/sync/glue/sync_backend_host.h

Index: chrome/browser/sync/glue/sync_backend_host.h
diff --git a/chrome/browser/sync/glue/sync_backend_host.h b/chrome/browser/sync/glue/sync_backend_host.h
index f632c16d9c27dfa9b5f70b680ecb680fa5459f4a..12d2a0cadfaa5eec5fd099dfed91e0845be25672 100644
--- a/chrome/browser/sync/glue/sync_backend_host.h
+++ b/chrome/browser/sync/glue/sync_backend_host.h
@@ -184,6 +184,10 @@ class SyncBackendHost : public BackendDataTypeConfigurer {
   // notifier.  This lasts until StopSyncingForShutdown() is called.
   void UpdateRegisteredInvalidationIds(const syncer::ObjectIdSet& ids);
 
+  // TODO(dcheng): Add a comment.
+  void AcknowledgeInvalidation(const invalidation::ObjectId& id,
+                               const syncer::AckHandle& ack_handle);
+
   // This starts the SyncerThread running a Syncer object to communicate with
   // sync servers.  Until this is called, no changes will leave or enter this
   // browser from the cloud / sync servers.