AudioDecoder: New method SampleRateHz, + implementations for our codecs

webrtc/modules/audio_coding/codecs/isac/audio_decoder_isac_t.h

Index: webrtc/modules/audio_coding/codecs/isac/audio_decoder_isac_t.h
diff --git a/webrtc/modules/audio_coding/codecs/isac/audio_decoder_isac_t.h b/webrtc/modules/audio_coding/codecs/isac/audio_decoder_isac_t.h
index b1907bbb394e214aa27620c093f54886f51a6a44..264cca2bf3885c67e7842ae966325c0b886ae1b5 100644
--- a/webrtc/modules/audio_coding/codecs/isac/audio_decoder_isac_t.h
+++ b/webrtc/modules/audio_coding/codecs/isac/audio_decoder_isac_t.h
@@ -14,18 +14,24 @@
 #include <vector>
 
 #include "webrtc/base/constructormagic.h"
+#include "webrtc/base/optional.h"
 #include "webrtc/base/scoped_ref_ptr.h"
 #include "webrtc/modules/audio_coding/codecs/audio_decoder.h"
 #include "webrtc/modules/audio_coding/codecs/isac/locked_bandwidth_info.h"
 
 namespace webrtc {
 
+// TODO(kwiberg): Remove the possibility of not specifying the sample rate at
+// object creation time.
 template <typename T>
 class AudioDecoderIsacT final : public AudioDecoder {
  public:
   AudioDecoderIsacT();
   explicit AudioDecoderIsacT(
       const rtc::scoped_refptr<LockedIsacBandwidthInfo>& bwinfo);
+  explicit AudioDecoderIsacT(int sample_rate_hz);
+  AudioDecoderIsacT(int sample_rate_hz,
+                    const rtc::scoped_refptr<LockedIsacBandwidthInfo>& bwinfo);
   ~AudioDecoderIsacT() override;
 
   bool HasDecodePlc() const override;
@@ -37,6 +43,7 @@ class AudioDecoderIsacT final : public AudioDecoder {
                      uint32_t rtp_timestamp,
                      uint32_t arrival_timestamp) override;
   int ErrorCode() override;
+  int SampleRateHz() const override;
   size_t Channels() const override;
   int DecodeInternal(const uint8_t* encoded,
                      size_t encoded_len,
@@ -45,9 +52,12 @@ class AudioDecoderIsacT final : public AudioDecoder {
                      SpeechType* speech_type) override;
 
  private:
+  AudioDecoderIsacT(rtc::Optional<int> sample_rate_hz,
+                    const rtc::scoped_refptr<LockedIsacBandwidthInfo>& bwinfo);
+
   typename T::instance_type* isac_state_;
+  rtc::Optional<int> sample_rate_hz_;
   rtc::scoped_refptr<LockedIsacBandwidthInfo> bwinfo_;
-  int decoder_sample_rate_hz_;
 
   RTC_DISALLOW_COPY_AND_ASSIGN(AudioDecoderIsacT);
 };