Add assignment operator to AudioEncoderRuntimeConfig

webrtc/modules/audio_coding/audio_network_adaptor/include/audio_network_adaptor_config.h

 /*
  *  Copyright (c) 2017 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.
  */
 
 #ifndef WEBRTC_MODULES_AUDIO_CODING_AUDIO_NETWORK_ADAPTOR_INCLUDE_AUDIO_NETWORK_ADAPTOR_CONFIG_H_
 #define WEBRTC_MODULES_AUDIO_CODING_AUDIO_NETWORK_ADAPTOR_INCLUDE_AUDIO_NETWORK_ADAPTOR_CONFIG_H_
 
 #include "webrtc/api/optional.h"
 
 namespace webrtc {
 
 struct AudioEncoderRuntimeConfig {
   AudioEncoderRuntimeConfig();
   AudioEncoderRuntimeConfig(const AudioEncoderRuntimeConfig& other);
+  AudioEncoderRuntimeConfig& operator=(const AudioEncoderRuntimeConfig& other);
   ~AudioEncoderRuntimeConfig();
   rtc::Optional<int> bitrate_bps;
   rtc::Optional<int> frame_length_ms;
   // Note: This is what we tell the encoder. It doesn't have to reflect
   // the actual NetworkMetrics; it's subject to our decision.
   rtc::Optional<float> uplink_packet_loss_fraction;
   rtc::Optional<bool> enable_fec;
   rtc::Optional<bool> enable_dtx;
 
   // Some encoders can encode fewer channels than the actual input to make
   // better use of the bandwidth. |num_channels| sets the number of channels
   // to encode.
   rtc::Optional<size_t> num_channels;
 };
 
 }  // namespace webrtc
 
 #endif  // WEBRTC_MODULES_AUDIO_CODING_AUDIO_NETWORK_ADAPTOR_INCLUDE_AUDIO_NETWORK_ADAPTOR_CONFIG_H_