Imported Optional from Chromium with some modifications.

webrtc/modules/audio_coding/neteq/decoder_database.cc

Index: webrtc/modules/audio_coding/neteq/decoder_database.cc
diff --git a/webrtc/modules/audio_coding/neteq/decoder_database.cc b/webrtc/modules/audio_coding/neteq/decoder_database.cc
index 165522f0dffb0851ad117e62654e2b60d5185f66..d5d3af4a4754e762a1077bfa2f8b58389dcd60a8 100644
--- a/webrtc/modules/audio_coding/neteq/decoder_database.cc
+++ b/webrtc/modules/audio_coding/neteq/decoder_database.cc
@@ -65,21 +65,17 @@ AudioDecoder* DecoderDatabase::DecoderInfo::GetDecoder(
 
 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;
   }
 }