Make key exchange strength available.

This change stores the size of the group/modulus (for RSA/DHE) or curve
ID (for ECDHE) in the |SSL_SESSION|. This makes it available for UIs
where desired.

Change-Id: I354141da432a08f71704c9683f298b361362483d
Reviewed-on: https://boringssl-review.googlesource.com/5280
Reviewed-by: Adam Langley <agl@google.com>
diff --git a/ssl/ssl_test.cc b/ssl/ssl_test.cc
index f31e5a1..bfb6b50 100644
--- a/ssl/ssl_test.cc
+++ b/ssl/ssl_test.cc
@@ -24,6 +24,8 @@
 #include <openssl/ssl.h>
 
 #include "test/scoped_types.h"
+#include "../crypto/test/test_util.h"
+
 
 struct ExpectedCipher {
   unsigned long id;
@@ -418,6 +420,8 @@
   if (encoded_len != input.size() ||
       memcmp(bssl::vector_data(&input), encoded.get(), input.size()) != 0) {
     fprintf(stderr, "SSL_SESSION_to_bytes did not round-trip\n");
+    hexdump(stderr, "Before: ", input.data(), input.size());
+    hexdump(stderr, "After:  ", encoded_raw, encoded_len);
     return false;
   }