Regression test for issue where Opus DTX status was being forgotten.

webrtc/modules/audio_coding/acm2/audio_coding_module.cc

Index: webrtc/modules/audio_coding/acm2/audio_coding_module.cc
diff --git a/webrtc/modules/audio_coding/acm2/audio_coding_module.cc b/webrtc/modules/audio_coding/acm2/audio_coding_module.cc
index b394c591567926b151b00a62c861f7f7bc35bbd1..b7441182e86d7bfef367e078a24c40ed66f72592 100644
--- a/webrtc/modules/audio_coding/acm2/audio_coding_module.cc
+++ b/webrtc/modules/audio_coding/acm2/audio_coding_module.cc
@@ -180,6 +180,8 @@ class AudioCodingModuleImpl final : public AudioCodingModule {
 
   int DisableOpusDtx() override;
 
+  int GetOpusDtx(bool* enabled) override;
+
   int UnregisterReceiveCodec(uint8_t payload_type) override;
 
   int EnableNack(size_t max_nack_list_size) override;
@@ -1205,6 +1207,15 @@ int AudioCodingModuleImpl::DisableOpusDtx() {
   return encoder_stack_->SetDtx(false) ? 0 : -1;
 }
 
+int AudioCodingModuleImpl::GetOpusDtx(bool* enabled) {
+  rtc::CritScope lock(&acm_crit_sect_);
+  if (!HaveValidEncoder("GetOpusDtx")) {
+    return -1;
+  }
+  *enabled = encoder_stack_->GetDtx();
+  return 0;
+}
+
 int32_t AudioCodingModuleImpl::PlayoutTimestamp(uint32_t* timestamp) {
   rtc::Optional<uint32_t> ts = PlayoutTimestamp();
   if (!ts)