Early connection migration in QUIC.

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 c8b01dabfcc97b59169b9daeb2110b3e6c4d07c0..8ba3f5b9c32a4ad8cfc68479ab5e3fc8bc027b22 100644
--- a/net/quic/quic_sent_packet_manager.cc
+++ b/net/quic/quic_sent_packet_manager.cc
@@ -36,6 +36,8 @@ static const int64_t kMaxRetransmissionTimeMs = 60000;
 static const size_t kMaxRetransmissions = 10;
 // Maximum number of packets retransmitted upon an RTO.
 static const size_t kMaxRetransmissionsOnTimeout = 2;
+// Minimum number of consecutive RTOs before path is considered to be degrading.
+const size_t kMinTimeoutsBeforePathDegrading = 2;
 
 // Ensure the handshake timer isnt't faster than 10ms.
 // This limits the tenth retransmitted packet to 10s after the initial CHLO.
@@ -622,6 +624,10 @@ void QuicSentPacketManager::OnRetransmissionTimeout() {
     case RTO_MODE:
       ++stats_->rto_count;
       RetransmitRtoPackets();
+      if (network_change_visitor_ != nullptr &&
+          consecutive_rto_count_ == kMinTimeoutsBeforePathDegrading) {
+        network_change_visitor_->OnPathDegrading();
+      }
       return;
   }
 }