Remove support for legacy TLS protocols by default

Now this requires explicitly passing the
WebRTC-LegacyTlsProtocols/Enabled/ field trial flag or an override.

Bug: webrtc:10261
Change-Id: Ib880bcc50cec0a21dcaa4784c228cacb020e5568
NOKEYCHECK: true
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/190282
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Commit-Queue: Guido Urdaneta <guidou@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#32488}
diff --git a/rtc_base/openssl_stream_adapter.cc b/rtc_base/openssl_stream_adapter.cc
index 5790b1b..f59b4ed 100644
--- a/rtc_base/openssl_stream_adapter.cc
+++ b/rtc_base/openssl_stream_adapter.cc
@@ -278,7 +278,7 @@
 bool ShouldAllowLegacyTLSProtocols() {
   return g_use_legacy_tls_protocols_override.load()
              ? g_allow_legacy_tls_protocols.load()
-             : !webrtc::field_trial::IsDisabled("WebRTC-LegacyTlsProtocols");
+             : webrtc::field_trial::IsEnabled("WebRTC-LegacyTlsProtocols");
 }
 
 OpenSSLStreamAdapter::OpenSSLStreamAdapter(