Convert more things to Array.

This adds a CopyFrom companion to Init as a replacement for CBS_stow.

Bug: 132
Change-Id: I4d77291b07552bd2286a09f8ba33655d6d97c853
Reviewed-on: https://boringssl-review.googlesource.com/20670
Reviewed-by: David Benjamin <davidben@google.com>
Commit-Queue: David Benjamin <davidben@google.com>
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>

ssl/ssl_lib.cc

diff --git a/ssl/ssl_lib.cc b/ssl/ssl_lib.cc
index 7a75776..262f9b2 100644
--- a/ssl/ssl_lib.cc
+++ b/ssl/ssl_lib.cc
@@ -2022,8 +2022,8 @@
     *out_types = NULL;
     return 0;
   }
-  *out_types = ssl->s3->hs->certificate_types;
-  return ssl->s3->hs->num_certificate_types;
+  *out_types = ssl->s3->hs->certificate_types.data();
+  return ssl->s3->hs->certificate_types.size();
 }
 
 EVP_PKEY *SSL_get_privatekey(const SSL *ssl) {