Add code counts for building version negotiation packets

This'll help us decide for how long we need to keep supporting older version negotiation formats.

PiperOrigin-RevId: 338719125
Change-Id: Ib9002c5879de3f9fa4cb19e7fc71ee8cb5f37367

quic/core/quic_framer.cc

diff --git a/quic/core/quic_framer.cc b/quic/core/quic_framer.cc
index cfa56c2..bd80cf3 100644
--- a/quic/core/quic_framer.cc
+++ b/quic/core/quic_framer.cc
@@ -1307,6 +1307,15 @@
     bool ietf_quic,
     bool use_length_prefix,
     const ParsedQuicVersionVector& versions) {
+  QUIC_CODE_COUNT(quic_build_version_negotiation);
+  if (use_length_prefix) {
+    DCHECK(ietf_quic);
+    QUIC_CODE_COUNT(quic_build_version_negotiation_ietf);
+  } else if (ietf_quic) {
+    QUIC_CODE_COUNT(quic_build_version_negotiation_old_ietf);
+  } else {
+    QUIC_CODE_COUNT(quic_build_version_negotiation_old_gquic);
+  }
   ParsedQuicVersionVector wire_versions = versions;
   // Add a version reserved for negotiation as suggested by the
   // "Using Reserved Versions" section of draft-ietf-quic-transport.