Add X509CertificateBytes which uses CRYPTO_BUFFER instead of macOS-native certificate types.

build/config/crypto.gni

Index: build/config/crypto.gni
diff --git a/build/config/crypto.gni b/build/config/crypto.gni
index 0196e873e506cc946532f6aa54eb8eb8f0eb988a..e07c16820c5b745547073a1455449a617a16c1d4 100644
--- a/build/config/crypto.gni
+++ b/build/config/crypto.gni
@@ -21,3 +21,9 @@ use_openssl_certs = is_android || is_nacl
 # True if NSS is used for certificate handling. It is possible to use OpenSSL
 # for the crypto library, but NSS for the platform certificate library.
 use_nss_certs = is_linux
+
+# True if certificates are represented with DER byte buffers. This can be true
+# in addition to use_openssl_certs or use_nss_certs, in that case byte certs
+# are used internally but OpenSSL or NSS are used for certificate verification.
+# TODO(mattm): crbug.com/671420: Implement and enable this for all platforms.
+use_byte_certs = is_mac

[mattm, 2017/03/29 01:19:11]

My thought is to land the CL with this set to false, and then do the flag flip
in a separate CL. That way if anything needs to be reverted it can just revert
the flag flip CL. Then sometime later the old x509_certificate_mac and related
code could be deleted.

The other option would just be to rip out x509_certificate_mac and other old
code right away, and just deal with a big revert if it happens to be necessary.

Any opinions?