Repair the CWND reduction caused by spurious RTO's in QUIC's congestion

net/quic/quic_sent_packet_manager.h

Index: net/quic/quic_sent_packet_manager.h
diff --git a/net/quic/quic_sent_packet_manager.h b/net/quic/quic_sent_packet_manager.h
index 2e75786119ac768c55be865214e01f7bff17149a..4c9bea92a3ad63dab876e578b36268e6d8844cb1 100644
--- a/net/quic/quic_sent_packet_manager.h
+++ b/net/quic/quic_sent_packet_manager.h
@@ -291,6 +291,9 @@ class NET_EXPORT_PRIVATE QuicSentPacketManager {
   scoped_ptr<LossDetectionInterface> loss_algorithm_;
 
   QuicPacketSequenceNumber largest_observed_;  // From the most recent ACK.
+  // Tracks the first RTO packet.  If any packet before that packet gets acked,
+  // it indicates the RTO was spurious and should be reversed(F-RTO).
+  QuicPacketSequenceNumber first_rto_transmission_;
   // Number of times the RTO timer has fired in a row without receiving an ack.
   size_t consecutive_rto_count_;
   // Number of times the tail loss probe has been sent.