Add GetDebugState() in SendAlgorithmInterface().

net/quic/core/quic_sent_packet_manager.cc

Index: net/quic/core/quic_sent_packet_manager.cc
diff --git a/net/quic/core/quic_sent_packet_manager.cc b/net/quic/core/quic_sent_packet_manager.cc
index 26ad049d15bd1ff046345675fe6fbfebaaa2cd99..0b0a8f873368e93597c2bcd5db37f34812280772 100644
--- a/net/quic/core/quic_sent_packet_manager.cc
+++ b/net/quic/core/quic_sent_packet_manager.cc
@@ -5,6 +5,7 @@
 #include "net/quic/core/quic_sent_packet_manager.h"
 
 #include <algorithm>
+#include <string>
 
 #include "base/logging.h"
 #include "base/stl_util.h"
@@ -921,6 +922,10 @@ QuicPacketCount QuicSentPacketManager::GetSlowStartThresholdInTcpMss() const {
   return send_algorithm_->GetSlowStartThreshold() / kDefaultTCPMSS;
 }
 
+std::string QuicSentPacketManager::GetDebugState() const {
+  return send_algorithm_->GetDebugState();
+}
+
 void QuicSentPacketManager::CancelRetransmissionsForStream(
     QuicStreamId stream_id) {
   unacked_packets_.CancelRetransmissionsForStream(stream_id);