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

sync/notifier/p2p_notifier.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "sync/notifier/p2p_notifier.h"
 
 #include <algorithm>
 
 #include "base/json/json_reader.h"
 #include "base/json/json_writer.h"
@@ skipping 263 matching lines @@
 
 void P2PNotifier::SendNotificationDataForTest(
     const P2PNotificationData& notification_data) {
   DCHECK(thread_checker_.CalledOnValidThread());
   SendNotificationData(notification_data);
 }
 
 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();
   DVLOG(1) << "Sending XMPP notification: " << notification.ToString();
   push_client_->SendNotification(notification);
 }
 
 }  // namespace syncer