In quicconnection, revert to a previously validated mtu after a delay equivalent to the duration of three ptos. protected by --gfe2_reloadable_flag_quic_revert_mtu_after_two_ptos.

PiperOrigin-RevId: 323411817
Change-Id: I1972673c2e75677fcffad3a45d9e0087e8fc6fc2
diff --git a/quic/test_tools/quic_connection_peer.h b/quic/test_tools/quic_connection_peer.h
index 258d953..8f3a78c 100644
--- a/quic/test_tools/quic_connection_peer.h
+++ b/quic/test_tools/quic_connection_peer.h
@@ -141,6 +141,9 @@
 
   static QuicTime GetBlackholeDetectionDeadline(QuicConnection* connection);
 
+  static QuicTime GetPathMtuReductionDetectionDeadline(
+      QuicConnection* connection);
+
   static QuicAlarm* GetIdleNetworkDetectorAlarm(QuicConnection* connection);
 
   static void SetServerConnectionId(