Remove the support of fallback from DTLS to SDES.

pc/peerconnectioninterface_unittest.cc

 /*
  *  Copyright 2012 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 2231 matching lines @@
   ASSERT_TRUE(content != NULL);
   EXPECT_FALSE(content->rejected);
 #ifdef HAVE_SCTP
   content =
       cricket::GetFirstDataContent(pc_->local_description()->description());
   ASSERT_TRUE(content != NULL);
   EXPECT_TRUE(content->rejected);
 #endif
 }
 
-// Test that an offer can be received which offers DTLS with SDES fallback.
-// Regression test for issue:
-// https://bugs.chromium.org/p/webrtc/issues/detail?id=6972
-TEST_F(PeerConnectionInterfaceTest, ReceiveDtlsSdesFallbackOffer) {
+// Test that fallback from DTLS to SDES is not supported.
+// The fallback was previously supported but was removed to simplify the code
+// and because it's non-standard.
+TEST_F(PeerConnectionInterfaceTest, DtlsSdesFallbackNotSupported) {
   FakeConstraints constraints;
   constraints.AddMandatory(webrtc::MediaConstraintsInterface::kEnableDtlsSrtp,
                            true);
   CreatePeerConnection(&constraints);
   // Wait for fake certificate to be generated. Previously, this is what caused
   // the "a=crypto" lines to be rejected.
   AddAudioVideoStream(kStreamLabel1, "audio_label", "video_label");
   ASSERT_NE(nullptr, fake_certificate_generator_);
   EXPECT_EQ_WAIT(1, fake_certificate_generator_->generated_certificates(),
                  kTimeout);
   std::unique_ptr<SessionDescriptionInterface> desc(
       webrtc::CreateSessionDescription(SessionDescriptionInterface::kOffer,
                                        kDtlsSdesFallbackSdp, nullptr));
-  EXPECT_TRUE(DoSetSessionDescription(std::move(desc), false));
-  CreateAnswerAsLocalDescription();
+  EXPECT_FALSE(DoSetSessionDescription(std::move(desc), false));
 }
 
 // Test that we can create an audio only offer and receive an answer with a
 // limited set of audio codecs and receive an updated offer with more audio
 // codecs, where the added codecs are not supported.
 TEST_F(PeerConnectionInterfaceTest, ReceiveUpdatedAudioOfferWithBadCodecs) {
   CreatePeerConnectionWithoutDtls();
   AddVoiceStream("audio_label");
   CreateOfferAsLocalDescription();
 
@@ skipping 1694 matching lines @@
   EXPECT_NE(a, f);
 
   PeerConnectionInterface::RTCConfiguration g;
   g.disable_ipv6 = true;
   EXPECT_NE(a, g);
 
   PeerConnectionInterface::RTCConfiguration h(
       PeerConnectionInterface::RTCConfigurationType::kAggressive);
   EXPECT_NE(a, h);
 }