Add GetDebugState() in SendAlgorithmInterface().

net/quic/core/congestion_control/send_algorithm_interface.h

Index: net/quic/core/congestion_control/send_algorithm_interface.h
diff --git a/net/quic/core/congestion_control/send_algorithm_interface.h b/net/quic/core/congestion_control/send_algorithm_interface.h
index 24efde367b14ff054def48070d2f62b75ef92230..8869ac265f43b3c55120b2437bbfbe6be795007a 100644
--- a/net/quic/core/congestion_control/send_algorithm_interface.h
+++ b/net/quic/core/congestion_control/send_algorithm_interface.h
@@ -117,6 +117,10 @@ class NET_EXPORT_PRIVATE SendAlgorithmInterface {
   virtual void ResumeConnectionState(
       const CachedNetworkParameters& cached_network_params,
       bool max_bandwidth_resumption) = 0;
+
+  // Retrieves debugging information about the current state of the
+  // send algorithm.
+  virtual std::string GetDebugState() const = 0;
 };
 
 }  // namespace net