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..3f404f736f31364f2b120c874efd3e8695b5a15d 100644
--- a/webrtc/modules/audio_coding/acm2/audio_coding_module.cc
+++ b/webrtc/modules/audio_coding/acm2/audio_coding_module.cc
@@ -48,6 +48,8 @@ class AudioCodingModuleImpl final : public AudioCodingModule {
   void ModifyEncoder(
       FunctionView<void(std::unique_ptr<AudioEncoder>*)> modifier) override;
 
+  void QueryEncoder(FunctionView<void(const AudioEncoder*)> query) override;
+
   // Get current send codec.
   rtc::Optional<CodecInst> SendCodec() const override;
 
@@ -596,6 +598,12 @@ void AudioCodingModuleImpl::ModifyEncoder(
   modifier(&encoder_stack_);
 }
 
+void AudioCodingModuleImpl::QueryEncoder(
+    FunctionView<void(const AudioEncoder*)> query) {
+  rtc::CritScope lock(&acm_crit_sect_);
+  query(encoder_stack_.get());
+}
+
 // Get current send codec.
 rtc::Optional<CodecInst> AudioCodingModuleImpl::SendCodec() const {
   rtc::CritScope lock(&acm_crit_sect_);