Add flag count macro for quic_enable_zero_rtt_for_tls

PiperOrigin-RevId: 321267446
Change-Id: I47f4b8040755b07469751055434c05bc360500cf

quic/core/tls_server_handshaker.cc

diff --git a/quic/core/tls_server_handshaker.cc b/quic/core/tls_server_handshaker.cc
index 717d774..054d174 100644
--- a/quic/core/tls_server_handshaker.cc
+++ b/quic/core/tls_server_handshaker.cc
@@ -381,6 +381,7 @@
     // FinishHandshake, we don't have any confirmation that the client is live,
     // so all end of handshake processing is deferred until the handshake is
     // actually complete.
+    QUIC_RELOADABLE_FLAG_COUNT(quic_enable_zero_rtt_for_tls);
     return;
   }
   if (!valid_alpn_received_) {