Move the stereo-disables-CNG logic from CodecManager to Rent-A-Codec

webrtc/modules/audio_coding/main/acm2/rent_a_codec.cc

 /*
  *  Copyright (c) 2015 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 241 matching lines @@
 AudioEncoder* RentACodec::RentEncoderStack(AudioEncoder* speech_encoder,
                                            StackParameters* param) {
   RTC_DCHECK(speech_encoder);
 
   auto pt = [&speech_encoder](const std::map<int, int>& m) {
     auto it = m.find(speech_encoder->SampleRateHz());
     return it == m.end() ? rtc::Optional<int>()
                          : rtc::Optional<int>(it->second);
   };
   auto cng_pt = pt(param->cng_payload_types);
-  param->use_cng = param->use_cng && cng_pt;
+  param->use_cng =
+      param->use_cng && cng_pt && speech_encoder->NumChannels() == 1;
   auto red_pt = pt(param->red_payload_types);
   param->use_red = param->use_red && red_pt;
 
   if (param->use_cng || param->use_red) {
     // The RED and CNG encoders need to be in sync with the speech encoder, so
     // reset the latter to ensure its buffer is empty.
     speech_encoder->Reset();
   }
   encoder_stack_ = speech_encoder;
   if (param->use_red) {
@@ skipping 13 matching lines @@
 }
 
 AudioDecoder* RentACodec::RentIsacDecoder() {
   if (!isac_decoder_)
     isac_decoder_ = CreateIsacDecoder(&isac_bandwidth_info_);
   return isac_decoder_.get();
 }
 
 }  // namespace acm2
 }  // namespace webrtc