Add GetDebugState() in SendAlgorithmInterface().

net/quic/core/quic_sent_packet_manager_interface.h

Index: net/quic/core/quic_sent_packet_manager_interface.h
diff --git a/net/quic/core/quic_sent_packet_manager_interface.h b/net/quic/core/quic_sent_packet_manager_interface.h
index e1f9d480bb71534eee526c3d95f68c7a931a2cda..61fb1cf69e2002bce8838c30bf8c79e48f0a4db7 100644
--- a/net/quic/core/quic_sent_packet_manager_interface.h
+++ b/net/quic/core/quic_sent_packet_manager_interface.h
@@ -152,6 +152,10 @@ class NET_EXPORT_PRIVATE QuicSentPacketManagerInterface {
   // TCP segments on the default path.
   virtual QuicPacketCount GetSlowStartThresholdInTcpMss() const = 0;
 
+  // Returns debugging information about the current state of the
+  // congestion controller.
+  virtual std::string GetDebugState() const = 0;
+
   // No longer retransmit data for |stream_id| on all paths.
   virtual void CancelRetransmissionsForStream(QuicStreamId stream_id) = 0;