Add an accessor for session->certs.

Chromium has some code which reaches into this field for memory
accounting.

This fixes a bug in doc.go where this line-wrapping confuses it. doc.go
needs a bit of a rewrite, but this is a bit better.

Change-Id: Ic9cc2c2fe9329d7bc366ccf91e0c9a92eae08ed2
Reviewed-on: https://boringssl-review.googlesource.com/27764
Commit-Queue: Steven Valdez <svaldez@google.com>
Reviewed-by: Steven Valdez <svaldez@google.com>
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>
diff --git a/ssl/ssl_session.cc b/ssl/ssl_session.cc
index a18ddd1..272fc55 100644
--- a/ssl/ssl_session.cc
+++ b/ssl/ssl_session.cc
@@ -913,6 +913,11 @@
   return session->x509_peer;
 }
 
+const STACK_OF(CRYPTO_BUFFER) *
+    SSL_SESSION_get0_peer_certificates(const SSL_SESSION *session) {
+  return session->certs;
+}
+
 size_t SSL_SESSION_get_master_key(const SSL_SESSION *session, uint8_t *out,
                                   size_t max_out) {
   // TODO(davidben): Fix master_key_length's type and remove these casts.