Adding Short Record Header feature.

net/socket/ssl_client_socket_impl.cc

Index: net/socket/ssl_client_socket_impl.cc
diff --git a/net/socket/ssl_client_socket_impl.cc b/net/socket/ssl_client_socket_impl.cc
index 97c67521063c9c9ba8d1545d9499aac6baec277f..4e3f71311c7c2a4974e2337bc0f583724f3b8a46 100644
--- a/net/socket/ssl_client_socket_impl.cc
+++ b/net/socket/ssl_client_socket_impl.cc
@@ -234,6 +234,9 @@ bool AreLegacyECDSACiphersEnabled() {
 }
 #endif
 
+const base::Feature kShortRecordHeaderFeature{
+    "SSLShortRecordHeader", base::FEATURE_DISABLED_BY_DEFAULT};

[davidben, 2017/01/02 10:48:10]

Should this go in testing/variations/fieldtrial_testing_config.json or something
like the TLS 1.3 negotiation was? (To that end, I probably should have put
SSLLegacyECDSACiphers in there. Oops.)

+
 }  // namespace
 
 class SSLClientSocketImpl::SSLContext {
@@ -289,6 +292,10 @@ class SSLClientSocketImpl::SSLContext {
 
     SSL_CTX_set_grease_enabled(ssl_ctx_.get(), 1);
 
+    if (base::FeatureList::IsEnabled(kShortRecordHeaderFeature)) {
+      SSL_CTX_set_short_header_enabled(ssl_ctx_.get(), 1);
+    }
+
     if (!SSL_CTX_add_client_custom_ext(ssl_ctx_.get(), kTbExtNum,
                                        &TokenBindingAddCallback,
                                        &TokenBindingFreeCallback, nullptr,