gfe-relnote: In GFE, export number of QUIC packets written per write operation. Protected by FLAGS_quic_export_server_num_packets_per_write_histogram.

PiperOrigin-RevId: 249251940
Change-Id: Ie92306bb1d10dec11c2801353026b363f3046d81

quic/core/quic_packet_generator.h

diff --git a/quic/core/quic_packet_generator.h b/quic/core/quic_packet_generator.h
index 6ea8215..327cc47 100644
--- a/quic/core/quic_packet_generator.h
+++ b/quic/core/quic_packet_generator.h
@@ -318,6 +318,11 @@
   // Whether crypto handshake packets should be fully padded.
   bool fully_pad_crypto_handshake_packets_;
 
+  // Packet number of the first packet of a write operation. This gets set
+  // when the out-most flusher attaches and gets cleared when the out-most
+  // flusher detaches.
+  QuicPacketNumber write_start_packet_number_;
+
   // Latched value of quic_deprecate_ack_bundling_mode.
   const bool deprecate_ack_bundling_mode_;