Add path_id to SerializedPacket. No functional change.

net/quic/quic_connection_test.cc

Index: net/quic/quic_connection_test.cc
diff --git a/net/quic/quic_connection_test.cc b/net/quic/quic_connection_test.cc
index ffe4f382f910ef3af8c4aadac8006ded2160358d..943a878de7092eef6e9790ea313360012ca79816 100644
--- a/net/quic/quic_connection_test.cc
+++ b/net/quic/quic_connection_test.cc
@@ -461,8 +461,8 @@ class TestConnection : public QuicConnection {
             ENCRYPTION_NONE, packet_number, *packet, buffer, kMaxPacketSize);
     delete packet;
     SerializedPacket serialized_packet(
-        packet_number, PACKET_6BYTE_PACKET_NUMBER, buffer, encrypted_length,
-        false, entropy_hash, retransmittable_frames, has_ack,
+        kDefaultPathId, packet_number, PACKET_6BYTE_PACKET_NUMBER, buffer,
+        encrypted_length, false, entropy_hash, retransmittable_frames, has_ack,
         has_pending_frames, ENCRYPTION_NONE);
     OnSerializedPacket(&serialized_packet);
   }