Implement TLS client auth in the OS X OpenSSL port.

net/BUILD.gn

Index: net/BUILD.gn
diff --git a/net/BUILD.gn b/net/BUILD.gn
index 07828b951028518a72a9e93e52f3453c1b20d1d7..49499abd57a7f7394bf2a74f6587d4a806866385 100644
--- a/net/BUILD.gn
+++ b/net/BUILD.gn
@@ -270,14 +270,17 @@ component("net") {
       "quic/crypto/p256_key_exchange_openssl.cc",
       "quic/crypto/scoped_evp_aead_ctx.cc",
       "quic/crypto/scoped_evp_aead_ctx.h",
-      "socket/openssl_ssl_util.cc",
-      "socket/openssl_ssl_util.h",
       "socket/ssl_client_socket_openssl.cc",
       "socket/ssl_client_socket_openssl.h",
       "socket/ssl_server_socket_openssl.cc",
       "socket/ssl_server_socket_openssl.h",
       "socket/ssl_session_cache_openssl.cc",
       "socket/ssl_session_cache_openssl.h",
+      "ssl/openssl_platform_key_mac.cc",
+      "ssl/openssl_platform_key_win.cc",
+      "ssl/openssl_platform_key.h",
+      "ssl/openssl_ssl_util.cc",
+      "ssl/openssl_ssl_util.h",
     ]
   }