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

webrtc/p2p/base/transportdescriptionfactory.cc

Index: webrtc/p2p/base/transportdescriptionfactory.cc
diff --git a/webrtc/p2p/base/transportdescriptionfactory.cc b/webrtc/p2p/base/transportdescriptionfactory.cc
index 61e2a9f3463bc16472bcfcbd01ef0f3d412712b2..238e1b66a14b46d0be228c6f613237d4c3798d95 100644
--- a/webrtc/p2p/base/transportdescriptionfactory.cc
+++ b/webrtc/p2p/base/transportdescriptionfactory.cc
@@ -110,7 +110,12 @@ bool TransportDescriptionFactory::SetSecurityInfo(
 
   // This digest algorithm is used to produce the a=fingerprint lines in SDP.
   // RFC 4572 Section 5 requires that those lines use the same hash function as
-  // the certificate's signature.
+  // the certificate's signature, which is what CreateFromCertificate does.
+  desc->identity_fingerprint.reset(
+      rtc::SSLFingerprint::CreateFromCertificate(certificate_));
+  if (!desc->identity_fingerprint) {
+    return false;
+  }
   std::string digest_alg;
   if (!certificate_->ssl_certificate().GetSignatureDigestAlgorithm(
           &digest_alg)) {