Remove the support of fallback from DTLS to SDES.

webrtc/pc/peerconnectioninterface_unittest.cc

Index: webrtc/pc/peerconnectioninterface_unittest.cc
diff --git a/webrtc/pc/peerconnectioninterface_unittest.cc b/webrtc/pc/peerconnectioninterface_unittest.cc
index c23a79d597b4fe8bdaec83edbd867df52ef3f3f5..64071cae9ec1ee7a019a759d9a8ef223eb7e8e5e 100644
--- a/webrtc/pc/peerconnectioninterface_unittest.cc
+++ b/webrtc/pc/peerconnectioninterface_unittest.cc
@@ -2248,10 +2248,8 @@ TEST_F(PeerConnectionInterfaceTest, ReceiveFireFoxOffer) {
 #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.

[Taylor Brandstetter, 2017/09/11 20:31:16]

Can you mention in the comment that this functionality was previously supported,
but was removed in order to simplify the code and because it's non-standard?

+TEST_F(PeerConnectionInterfaceTest, DtlsSdesFallbackNotSupport) {

[Taylor Brandstetter, 2017/09/11 20:31:16]

nit: "NotSupported" instead of "NotSupport"

   FakeConstraints constraints;
   constraints.AddMandatory(webrtc::MediaConstraintsInterface::kEnableDtlsSrtp,
                            true);
@@ -2264,8 +2262,7 @@ TEST_F(PeerConnectionInterfaceTest, ReceiveDtlsSdesFallbackOffer) {
                  kTimeout);
   SessionDescriptionInterface* desc = webrtc::CreateSessionDescription(
       SessionDescriptionInterface::kOffer, kDtlsSdesFallbackSdp, nullptr);
-  EXPECT_TRUE(DoSetSessionDescription(desc, false));
-  CreateAnswerAsLocalDescription();
+  EXPECT_FALSE(DoSetSessionDescription(desc, false));
 }
 
 // Test that we can create an audio only offer and receive an answer with a