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

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 97dc00d7a6854bf6ee5ccc24b56177d6dd8ddc5c..41803f754ac116a2ecf0d3e4e4f3a6138fe7a9f5 100644
--- a/webrtc/modules/audio_coding/neteq/decoder_database.cc
+++ b/webrtc/modules/audio_coding/neteq/decoder_database.cc
@@ -150,10 +150,10 @@ bool DecoderDatabase::IsType(uint8_t rtp_payload_type,
 }
 
 bool DecoderDatabase::IsComfortNoise(uint8_t rtp_payload_type) const {
-  if (IsType(rtp_payload_type, kDecoderCNGnb) ||
-      IsType(rtp_payload_type, kDecoderCNGwb) ||
-      IsType(rtp_payload_type, kDecoderCNGswb32kHz) ||
-      IsType(rtp_payload_type, kDecoderCNGswb48kHz)) {
+  if (IsType(rtp_payload_type, NetEqDecoder::kDecoderCNGnb) ||
+      IsType(rtp_payload_type, NetEqDecoder::kDecoderCNGwb) ||
+      IsType(rtp_payload_type, NetEqDecoder::kDecoderCNGswb32kHz) ||
+      IsType(rtp_payload_type, NetEqDecoder::kDecoderCNGswb48kHz)) {
     return true;
   } else {
     return false;
@@ -161,11 +161,11 @@ bool DecoderDatabase::IsComfortNoise(uint8_t rtp_payload_type) const {
 }
 
 bool DecoderDatabase::IsDtmf(uint8_t rtp_payload_type) const {
-  return IsType(rtp_payload_type, kDecoderAVT);
+  return IsType(rtp_payload_type, NetEqDecoder::kDecoderAVT);
 }
 
 bool DecoderDatabase::IsRed(uint8_t rtp_payload_type) const {
-  return IsType(rtp_payload_type, kDecoderRED);
+  return IsType(rtp_payload_type, NetEqDecoder::kDecoderRED);
 }
 
 int DecoderDatabase::SetActiveDecoder(uint8_t rtp_payload_type,