Add ClientHello no_session_id variant.

Change-Id: I3d249582dea871d7b1c078a6b5f57679037d1b8f
Reviewed-on: https://boringssl-review.googlesource.com/17984
Reviewed-by: Steven Valdez <svaldez@google.com>
Commit-Queue: Steven Valdez <svaldez@google.com>

ssl/handshake_client.cc

diff --git a/ssl/handshake_client.cc b/ssl/handshake_client.cc
index 10c10a2..e60b6ae 100644
--- a/ssl/handshake_client.cc
+++ b/ssl/handshake_client.cc
@@ -764,7 +764,8 @@
     return -1;
   }
 
-  /* Initialize a random session ID for the experimental TLS 1.3 variant. */
+  /* Initialize a random session ID for the experimental TLS 1.3 variant
+   * requiring a session id. */
   if (ssl->tls13_variant == tls13_experiment) {
     hs->session_id_len = sizeof(hs->session_id);
     if (!RAND_bytes(hs->session_id, hs->session_id_len)) {