[Sync] Don't send notifications with no changed types

sync/notifier/p2p_notifier.cc

Index: sync/notifier/p2p_notifier.cc
diff --git a/sync/notifier/p2p_notifier.cc b/sync/notifier/p2p_notifier.cc
index c4fcfbe649eab9dd939630969d76165031d42984..bb16f5e21d97ea1c787d4909d6b50266a3f29c4e 100644
--- a/sync/notifier/p2p_notifier.cc
+++ b/sync/notifier/p2p_notifier.cc
@@ -281,6 +281,11 @@ void P2PNotifier::SendNotificationDataForTest(
 void P2PNotifier::SendNotificationData(
     const P2PNotificationData& notification_data) {
   DCHECK(thread_checker_.CalledOnValidThread());
+  if (notification_data.GetChangedTypes().Empty()) {
+    DVLOG(1) << "Not sending XMPP notification with no changed types: "
+             << notification_data.ToString();
+    return;
+  }
   notifier::Notification notification;
   notification.channel = kSyncP2PNotificationChannel;
   notification.data = notification_data.ToString();