AudioDecoder: New method SampleRateHz, + implementations for our codecs

webrtc/modules/audio_coding/codecs/g711/audio_decoder_pcm.cc

Index: webrtc/modules/audio_coding/codecs/g711/audio_decoder_pcm.cc
diff --git a/webrtc/modules/audio_coding/codecs/g711/audio_decoder_pcm.cc b/webrtc/modules/audio_coding/codecs/g711/audio_decoder_pcm.cc
index 9757b4a0100674095353e9e20e43f986a1b3aba8..0f85215b4d01e459c1ff69248b74565a2acab066 100644
--- a/webrtc/modules/audio_coding/codecs/g711/audio_decoder_pcm.cc
+++ b/webrtc/modules/audio_coding/codecs/g711/audio_decoder_pcm.cc
@@ -16,6 +16,10 @@ namespace webrtc {
 
 void AudioDecoderPcmU::Reset() {}
 
+int AudioDecoderPcmU::SampleRateHz() const {
+  return sample_rate_hz_;
+}
+
 size_t AudioDecoderPcmU::Channels() const {
   return num_channels_;
 }
@@ -40,6 +44,10 @@ int AudioDecoderPcmU::PacketDuration(const uint8_t* encoded,
 
 void AudioDecoderPcmA::Reset() {}
 
+int AudioDecoderPcmA::SampleRateHz() const {
+  return sample_rate_hz_;
+}
+
 size_t AudioDecoderPcmA::Channels() const {
   return num_channels_;
 }