Add SSL_get_server_key_exchange_hash.

This exposes the ServerKeyExchange signature hash type used in the most recent
handshake, for histogramming on the client.

BUG=549662

Change-Id: I8a4e00ac735b1ecd2c2df824112c3a0bc62332a7
Reviewed-on: https://boringssl-review.googlesource.com/6413
Reviewed-by: Adam Langley <agl@google.com>
diff --git a/ssl/test/test_config.cc b/ssl/test/test_config.cc
index 8b540c3..50e6b23 100644
--- a/ssl/test/test_config.cc
+++ b/ssl/test/test_config.cc
@@ -141,6 +141,8 @@
   { "-mtu", &TestConfig::mtu },
   { "-export-keying-material", &TestConfig::export_keying_material },
   { "-expect-total-renegotiations", &TestConfig::expect_total_renegotiations },
+  { "-expect-server-key-exchange-hash",
+    &TestConfig::expect_server_key_exchange_hash },
 };
 
 }  // namespace