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

net/quic/quic_sent_packet_manager_interface.h

Index: net/quic/quic_sent_packet_manager_interface.h
diff --git a/net/quic/quic_sent_packet_manager_interface.h b/net/quic/quic_sent_packet_manager_interface.h
index 4cfd8393c1a781b2e2580a947457ca5dfcdac316..e60f8ef24b94ccd43d327043bcec7736b6e49cee 100644
--- a/net/quic/quic_sent_packet_manager_interface.h
+++ b/net/quic/quic_sent_packet_manager_interface.h
@@ -54,6 +54,9 @@ class NET_EXPORT_PRIVATE QuicSentPacketManagerInterface {
     // TODO(jri): With multipath, this method should probably have a path_id
     // parameter, and should maybe result in the path being marked as inactive.
     virtual void OnPathDegrading() = 0;
+
+    // Called when the Path MTU may have increased.
+    virtual void OnPathMtuIncreased(QuicPacketLength packet_size) = 0;
   };
 
   virtual ~QuicSentPacketManagerInterface() {}