Imported Optional from Chromium with some modifications.

webrtc/modules/audio_coding/neteq/decoder_database.cc

 /*
  *  Copyright (c) 2012 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 47 matching lines @@
   RTC_DCHECK(audio_format_);
   if (!decoder_) {
     decoder_ = factory->MakeAudioDecoder(*audio_format_);
   }
   RTC_DCHECK(decoder_) << "Failed to create: " << *audio_format_;
   return decoder_.get();
 }
 
 rtc::Optional<DecoderDatabase::DecoderInfo::CngDecoder>
 DecoderDatabase::DecoderInfo::CngDecoder::Create(NetEqDecoder ct) {
-  const auto cng = [](int sample_rate_hz) {
-    return rtc::Optional<DecoderDatabase::DecoderInfo::CngDecoder>(
-        {sample_rate_hz});
-  };
   switch (ct) {
     case NetEqDecoder::kDecoderCNGnb:
-      return cng(8000);
+      return CngDecoder{8000};
     case NetEqDecoder::kDecoderCNGwb:
-      return cng(16000);
+      return CngDecoder{16000};
     case NetEqDecoder::kDecoderCNGswb32kHz:
-      return cng(32000);
+      return CngDecoder{32000};
     case NetEqDecoder::kDecoderCNGswb48kHz:
-      return cng(48000);
+      return CngDecoder{48000};
     default:
-      return rtc::Optional<DecoderDatabase::DecoderInfo::CngDecoder>();
+      return rtc::nullopt;
   }
 }
 
 bool DecoderDatabase::Empty() const { return decoders_.empty(); }
 
 int DecoderDatabase::Size() const { return static_cast<int>(decoders_.size()); }
 
 void DecoderDatabase::Reset() {
   decoders_.clear();
   active_decoder_type_ = -1;
@@ skipping 203 matching lines @@
       LOG(LS_WARNING) << "CheckPayloadTypes: unknown RTP payload type "
                       << static_cast<int>((*it)->header.payloadType);
       return kDecoderNotFound;
     }
   }
   return kOK;
 }
 
 
 }  // namespace webrtc