Simplify RTO interaction between the QUIC sent packet manager and the

net/quic/congestion_control/tcp_cubic_sender.cc

Index: net/quic/congestion_control/tcp_cubic_sender.cc
diff --git a/net/quic/congestion_control/tcp_cubic_sender.cc b/net/quic/congestion_control/tcp_cubic_sender.cc
index c1828005e583614edd541b1dace98c52898c11e1..0cca50487228962b55613feb432f90c35fe338ea 100644
--- a/net/quic/congestion_control/tcp_cubic_sender.cc
+++ b/net/quic/congestion_control/tcp_cubic_sender.cc
@@ -277,9 +277,12 @@ void TcpCubicSender::CongestionAvoidance(QuicPacketSequenceNumber ack) {
   }
 }
 
-void TcpCubicSender::OnRetransmissionTimeout() {
-  cubic_.Reset();
-  congestion_window_ = kMinimumCongestionWindow;
+void TcpCubicSender::OnRetransmissionTimeout(bool packets_retransmitted) {
+  bytes_in_flight_ = 0;
+  if (packets_retransmitted) {
+    cubic_.Reset();
+    congestion_window_ = kMinimumCongestionWindow;
+  }
 }
 
 void TcpCubicSender::AckAccounting(QuicTime::Delta rtt) {