Add original_path_id to SerializedPacket and OnPacketSent. No functional change expected.

net/quic/quic_packet_creator.cc

Index: net/quic/quic_packet_creator.cc
diff --git a/net/quic/quic_packet_creator.cc b/net/quic/quic_packet_creator.cc
index 4687f71d26760d8c25b656688e5852bfc730da0b..686fed285aa346abec8bdbf36b73736f98e9583f 100644
--- a/net/quic/quic_packet_creator.cc
+++ b/net/quic/quic_packet_creator.cc
@@ -318,6 +318,7 @@ void QuicPacketCreator::ReserializeAllFrames(
     DCHECK(success);
   }
   SerializePacket(buffer, buffer_len);
+  packet_.original_path_id = retransmission.path_id;
   packet_.original_packet_number = retransmission.packet_number;
   packet_.transmission_type = retransmission.transmission_type;
   OnSerializedPacket();
@@ -363,6 +364,7 @@ void QuicPacketCreator::ClearPacket() {
   packet_.has_stop_waiting = false;
   packet_.has_crypto_handshake = NOT_HANDSHAKE;
   packet_.num_padding_bytes = 0;
+  packet_.original_path_id = kInvalidPathId;
   packet_.original_packet_number = 0;
   packet_.transmission_type = NOT_RETRANSMISSION;
   packet_.encrypted_buffer = nullptr;