Only set certificate on DTLS transport if fingerprint is found in SDP.

webrtc/p2p/base/transportcontroller.cc

Index: webrtc/p2p/base/transportcontroller.cc
diff --git a/webrtc/p2p/base/transportcontroller.cc b/webrtc/p2p/base/transportcontroller.cc
index 820645b42b7dc7589cb35423a1d0d363d0fbe10d..1dc21180ad93ad888201c7e942fbafb8fa9c4ec4 100644
--- a/webrtc/p2p/base/transportcontroller.cc
+++ b/webrtc/p2p/base/transportcontroller.cc
@@ -262,10 +262,6 @@ DtlsTransportInternal* TransportController::CreateDtlsTransport_n(
   dtls->ice_transport()->SetIceRole(ice_role_);
   dtls->ice_transport()->SetIceTiebreaker(ice_tiebreaker_);
   dtls->ice_transport()->SetIceConfig(ice_config_);
-  if (certificate_) {
-    bool set_cert_success = dtls->SetLocalCertificate(certificate_);
-    RTC_DCHECK(set_cert_success);
-  }
 
   // Connect to signals offered by the channels. Currently, the DTLS channel
   // forwards signals from the ICE channel, so we only need to connect to the
@@ -539,16 +535,13 @@ bool TransportController::SetLocalCertificate_n(
   }
   certificate_ = certificate;
 
-  // Set certificate both for Transport, which verifies it matches the
-  // fingerprint in SDP...
+  // Set certificate for JsepTransport, which verifies it matches the
+  // fingerprint in SDP, and only applies it to the DTLS transport if a
+  // fingerprint attribute is present in SDP. This is used for fallback from
+  // DTLS to SDES.
   for (auto& kv : transports_) {
     kv.second->SetLocalCertificate(certificate_);
   }
-  // ... and for the DTLS channel, which needs it for the DTLS handshake.
-  for (auto& channel : channels_) {
-    bool set_cert_success = channel->dtls()->SetLocalCertificate(certificate);
-    RTC_DCHECK(set_cert_success);
-  }
   return true;
 }