net: enable SSL_MODE_CBC_RECORD_SPLITTING with OpenSSL.

This enables 1/n-1 record splitting, which we have done with NSS for a
long time. No compat issues are expected with this.

(This does not appear to be a regression from the OpenSSL -> BoringSSL
switch as I don't see that a record splitting patch was previously
included.)

BUG=none

Review URL: https://codereview.chromium.org/508803003

Cr-Commit-Position: refs/heads/master@{#292197}

net/socket/ssl_client_socket_openssl.cc

@@ -744,6 +744,7 @@ int SSLClientSocketOpenSSL::Init() {
   SslSetClearMask mode;
 
   mode.ConfigureFlag(SSL_MODE_RELEASE_BUFFERS, true);
+  mode.ConfigureFlag(SSL_MODE_CBC_RECORD_SPLITTING, true);
 
   mode.ConfigureFlag(SSL_MODE_HANDSHAKE_CUTTHROUGH,
                      ssl_config_.false_start_enabled);