Enable NACK for audio even if there are no send streams.

webrtc/media/engine/webrtcvoiceengine_unittest.cc

 /*
  *  Copyright (c) 2008 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 1284 matching lines @@
 TEST_F(WebRtcVoiceEngineTestFake, SetSendCodecEnableNackAsCallee) {
   EXPECT_TRUE(SetupRecvStream());
   int channel_num = voe_.GetLastChannel();
   cricket::AudioSendParameters parameters;
   parameters.codecs.push_back(kOpusCodec);
   parameters.codecs[0].AddFeedbackParam(
       cricket::FeedbackParam(cricket::kRtcpFbParamNack,
                              cricket::kParamValueEmpty));
   EXPECT_FALSE(voe_.GetNACK(channel_num));
   EXPECT_TRUE(channel_->SetSendParameters(parameters));
-  EXPECT_FALSE(voe_.GetNACK(channel_num));
+  // NACK should be enabled even with no send stream.
+  EXPECT_TRUE(voe_.GetNACK(channel_num));
 
   EXPECT_TRUE(channel_->AddSendStream(
       cricket::StreamParams::CreateLegacy(kSsrc1)));
   EXPECT_TRUE(voe_.GetNACK(voe_.GetLastChannel()));
 }
 
 // Test that we can enable NACK on receive streams.
 TEST_F(WebRtcVoiceEngineTestFake, SetSendCodecEnableNackRecvStreams) {
   EXPECT_TRUE(SetupSendStream());
   int channel_num1 = voe_.GetLastChannel();
@@ skipping 2280 matching lines @@
 TEST(WebRtcVoiceEngineTest, SetRecvCodecs) {
   cricket::WebRtcVoiceEngine engine(nullptr);
   std::unique_ptr<webrtc::Call> call(
       webrtc::Call::Create(webrtc::Call::Config()));
   cricket::WebRtcVoiceMediaChannel channel(&engine, cricket::MediaConfig(),
                                            cricket::AudioOptions(), call.get());
   cricket::AudioRecvParameters parameters;
   parameters.codecs = engine.codecs();
   EXPECT_TRUE(channel.SetRecvParameters(parameters));
 }