Update from https://crrev.com/311346

net/quic/quic_sent_packet_manager.cc

Index: net/quic/quic_sent_packet_manager.cc
diff --git a/net/quic/quic_sent_packet_manager.cc b/net/quic/quic_sent_packet_manager.cc
index b71b300684adc8f1d29852ec7a432be94ccffc29..f2c514b4bcc0b09891ab4413d256e9ac9279be26 100644
--- a/net/quic/quic_sent_packet_manager.cc
+++ b/net/quic/quic_sent_packet_manager.cc
@@ -467,9 +467,10 @@ void QuicSentPacketManager::MarkPacketRevived(
 
   // The AckNotifierManager needs to be notified for revived packets,
   // since it indicates the packet arrived from the appliction's perspective.
-  if (transmission_info.retransmittable_frames) {
-    ack_notifier_manager_.OnPacketAcked(
-        newest_transmission, delta_largest_observed);
+  if (FLAGS_quic_attach_ack_notifiers_to_packets ||
+      transmission_info.retransmittable_frames) {
+    ack_notifier_manager_.OnPacketAcked(newest_transmission,
+                                        delta_largest_observed);
   }
 
   unacked_packets_.RemoveRetransmittability(sequence_number);