NetEq decoder database: Don't keep track of sample rate for builtin decoders

webrtc/modules/audio_coding/neteq/decoder_database.h

Index: webrtc/modules/audio_coding/neteq/decoder_database.h
diff --git a/webrtc/modules/audio_coding/neteq/decoder_database.h b/webrtc/modules/audio_coding/neteq/decoder_database.h
index 72b43df5b31792d7cc81dbf10e70925767694639..4169dc2b1b7d96f9ed2295c4ce546e8623ebb7fe 100644
--- a/webrtc/modules/audio_coding/neteq/decoder_database.h
+++ b/webrtc/modules/audio_coding/neteq/decoder_database.h
@@ -41,9 +41,10 @@ class DecoderDatabase {
   // Class that stores decoder info in the database.
   class DecoderInfo {
    public:
+    DecoderInfo(NetEqDecoder ct, const std::string& nm);
     DecoderInfo(NetEqDecoder ct,
                 const std::string& nm,
-                int fs,
+                int sample_rate_hz,
                 AudioDecoder* ext_dec);
     DecoderInfo(DecoderInfo&&);
     ~DecoderInfo();
@@ -55,14 +56,35 @@ class DecoderDatabase {
     // always recreate it later if we need it.)
     void DropDecoder() { decoder_.reset(); }
 
+    int SampleRateHz() const {
+      RTC_DCHECK_EQ(1, !!decoder_ + !!external_decoder + !!cng_decoder_);
+      return decoder_ ? decoder_->SampleRateHz()
+                      : external_decoder ? external_decoder->sample_rate_hz
+                                         : cng_decoder_->sample_rate_hz;
+    }
+
     const NetEqDecoder codec_type;
     const std::string name;
-    const int fs_hz;
-    AudioDecoder* const external_decoder;
 
    private:
     const rtc::Optional<SdpAudioFormat> audio_format_;
     std::unique_ptr<AudioDecoder> decoder_;
+
+    // Set iff this is an external decoder.
+    struct ExternalDecoder {
+      // TODO(kwiberg): Remove sample_rate_hz once we can trust all decoders to
+      // implement SampleRateHz().
+      int sample_rate_hz;
+      AudioDecoder* decoder;
+    };
+    const rtc::Optional<ExternalDecoder> external_decoder;
+
+    // Set iff this is a comfort noise decoder.
+    struct CngDecoder {
+      static rtc::Optional<CngDecoder> Create(NetEqDecoder ct);
+      int sample_rate_hz;
+    };
+    const rtc::Optional<CngDecoder> cng_decoder_;
   };
 
   // Maximum value for 8 bits, and an invalid RTP payload type (since it is