Add a merely pass-through QuicMultipathSentPacketManager. Protected behind blocked flag FLAGS_quic_…

net/quic/test_tools/quic_connection_peer.h

Index: net/quic/test_tools/quic_connection_peer.h
diff --git a/net/quic/test_tools/quic_connection_peer.h b/net/quic/test_tools/quic_connection_peer.h
index 30af9148930c8a25a4662375d9a9c708a24de5e5..6433c471c523bcc37bda9eb55965d832774f1780 100644
--- a/net/quic/test_tools/quic_connection_peer.h
+++ b/net/quic/test_tools/quic_connection_peer.h
@@ -35,9 +35,16 @@ class QuicConnectionPeer {
  public:
   static void SendAck(QuicConnection* connection);
 
+  // Sets send algorithm of |path_id|.
   static void SetSendAlgorithm(QuicConnection* connection,
+                               QuicPathId path_id,
                                SendAlgorithmInterface* send_algorithm);
 
+  // Sets loss algorithm of |path_id|.
+  static void SetLossAlgorithm(QuicConnection* connection,
+                               QuicPathId path_id,
+                               LossDetectionInterface* loss_algorithm);
+
   static const QuicFrame GetUpdatedAckFrame(QuicConnection* connection);
 
   static void PopulateStopWaitingFrame(QuicConnection* connection,
@@ -49,8 +56,9 @@ class QuicConnectionPeer {
 
   static QuicPacketGenerator* GetPacketGenerator(QuicConnection* connection);
 
-  static QuicSentPacketManager* GetSentPacketManager(
-      QuicConnection* connection);
+  // Returns sent packet manager of |path_id|.
+  static QuicSentPacketManager* GetSentPacketManager(QuicConnection* connection,
+                                                     QuicPathId path_id);
 
   static QuicTime::Delta GetNetworkTimeout(QuicConnection* connection);