Add path_id to SerializedPacket. No functional change.

net/quic/quic_protocol.h

Index: net/quic/quic_protocol.h
diff --git a/net/quic/quic_protocol.h b/net/quic/quic_protocol.h
index 36f9c2d4dfc1c550c90e6bf4f471823c1d7bca1a..a7ac1f6ab12ec872d322b29765f23ddc6f86d4f4 100644
--- a/net/quic/quic_protocol.h
+++ b/net/quic/quic_protocol.h
@@ -194,6 +194,8 @@ const uint64 kUFloat16MaxValue =  // 0x3FFC0000000
 
 // Default path ID.
 const QuicPathId kDefaultPathId = 0;
+// Invalid path ID.
+const QuicPathId kInvalidPathId = -1;
 
 enum TransmissionType {
   NOT_RETRANSMISSION,
@@ -1197,14 +1199,16 @@ struct NET_EXPORT_PRIVATE AckListenerWrapper {
 };
 
 struct NET_EXPORT_PRIVATE SerializedPacket {
-  SerializedPacket(QuicPacketNumber packet_number,
+  SerializedPacket(QuicPathId path_id,
+                   QuicPacketNumber packet_number,
                    QuicPacketNumberLength packet_number_length,
                    QuicEncryptedPacket* packet,
                    QuicPacketEntropyHash entropy_hash,
                    RetransmittableFrames* retransmittable_frames,
                    bool has_ack,
                    bool has_stop_waiting);
-  SerializedPacket(QuicPacketNumber packet_number,
+  SerializedPacket(QuicPathId path_id,
+                   QuicPacketNumber packet_number,
                    QuicPacketNumberLength packet_number_length,
                    char* encrypted_buffer,
                    size_t encrypted_length,
@@ -1218,6 +1222,7 @@ struct NET_EXPORT_PRIVATE SerializedPacket {
 
   QuicEncryptedPacket* packet;
   RetransmittableFrames* retransmittable_frames;
+  QuicPathId path_id;
   QuicPacketNumber packet_number;
   QuicPacketNumberLength packet_number_length;
   EncryptionLevel encryption_level;