Replace QUIC's PathMtuAckListener with a non-AckListener approach. Protected by FLAGS_quic_no_mtu_d…

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 7544747c389cc2c9668131da3139f6f3a921edd2..33e79fec8772c65adcd7e6b5f814231888a06c8b 100644
--- a/net/quic/quic_sent_packet_manager.cc
+++ b/net/quic/quic_sent_packet_manager.cc
@@ -93,6 +93,7 @@ QuicSentPacketManager::QuicSentPacketManager(
       use_new_rto_(false),
       undo_pending_retransmits_(false),
       largest_newly_acked_(0),
+      largest_mtu_acked_(0),
       handshake_confirmed_(false) {}
 
 QuicSentPacketManager::~QuicSentPacketManager() {}
@@ -529,6 +530,12 @@ void QuicSentPacketManager::MarkPacketHandled(QuicPacketNumber packet_number,
     }
   }
 
+  if (FLAGS_quic_no_mtu_discovery_ack_listener &&
+      network_change_visitor_ != nullptr &&
+      info->bytes_sent > largest_mtu_acked_) {
+    largest_mtu_acked_ = info->bytes_sent;
+    network_change_visitor_->OnPathMtuIncreased(largest_mtu_acked_);
+  }
   unacked_packets_.RemoveFromInFlight(info);
   unacked_packets_.RemoveRetransmittability(info);
   if (FLAGS_quic_loss_recovery_use_largest_acked) {