Audio Coding Module: Use separate instances for 16 kHz and 32 kHz iSAC decoder

webrtc/modules/audio_coding/acm2/audio_coding_module_impl.h

Index: webrtc/modules/audio_coding/acm2/audio_coding_module_impl.h
diff --git a/webrtc/modules/audio_coding/acm2/audio_coding_module_impl.h b/webrtc/modules/audio_coding/acm2/audio_coding_module_impl.h
index 63dfb8105670824c9b4452be6ab15aa6ef80702b..5ae6677cf9fd7f052f1dd42c0bd4e36209e9eb7f 100644
--- a/webrtc/modules/audio_coding/acm2/audio_coding_module_impl.h
+++ b/webrtc/modules/audio_coding/acm2/audio_coding_module_impl.h
@@ -268,7 +268,8 @@ class AudioCodingModuleImpl final : public AudioCodingModule {
   // RegisterEncoder.
   std::unique_ptr<AudioEncoder> encoder_stack_ GUARDED_BY(acm_crit_sect_);
 
-  std::unique_ptr<AudioDecoder> isac_decoder_ GUARDED_BY(acm_crit_sect_);
+  std::unique_ptr<AudioDecoder> isac_decoder_16k_ GUARDED_BY(acm_crit_sect_);
+  std::unique_ptr<AudioDecoder> isac_decoder_32k_ GUARDED_BY(acm_crit_sect_);
 
   // This is to keep track of CN instances where we can send DTMFs.
   uint8_t previous_pltype_ GUARDED_BY(acm_crit_sect_);