Make an enum class out of NetEqDecoder, and hide the neteq_decoders_ table

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 37 matching lines @@
 
 bool RentACodec::IsCodecValid(const CodecInst& codec_inst) {
   return ACMCodecDB::CodecNumber(codec_inst) >= 0;
 }
 
 rtc::ArrayView<const CodecInst> RentACodec::Database() {
   return rtc::ArrayView<const CodecInst>(ACMCodecDB::database_,
                                          NumberOfCodecs());
 }
 
+rtc::Maybe<NetEqDecoder> RentACodec::NetEqDecoderFromCodecId(CodecId codec_id,
+                                                             int num_channels) {
+  rtc::Maybe<int> i = CodecIndexFromId(codec_id);
+  if (!i)
+    return rtc::Maybe<NetEqDecoder>();
+  const NetEqDecoder ned = ACMCodecDB::neteq_decoders_[*i];
+  return (ned == NetEqDecoder::kDecoderOpus && num_channels == 2)
+             ? NetEqDecoder::kDecoderOpus_2ch
+             : ned;
+}
+
 }  // namespace acm2
 }  // namespace webrtc