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

webrtc/modules/audio_coding/include/audio_coding_module.h

Index: webrtc/modules/audio_coding/include/audio_coding_module.h
diff --git a/webrtc/modules/audio_coding/include/audio_coding_module.h b/webrtc/modules/audio_coding/include/audio_coding_module.h
index 5b35bcf7a5443317343a7d003ad1ec28458f874c..30a17f72ea6bf3ed63ee314b36ae34817bb83b3e 100644
--- a/webrtc/modules/audio_coding/include/audio_coding_module.h
+++ b/webrtc/modules/audio_coding/include/audio_coding_module.h
@@ -250,6 +250,10 @@ class AudioCodingModule {
   virtual void ModifyEncoder(
       FunctionView<void(std::unique_ptr<AudioEncoder>*)> modifier) = 0;
 
+  // |modifier| is called exactly once with one argument: a const pointer to the
+  // current encoder (which is null if there is no current encoder).
+  virtual void QueryEncoder(FunctionView<void(AudioEncoder const*)> query) = 0;
+
   // Utility method for simply replacing the existing encoder with a new one.
   void SetEncoder(std::unique_ptr<AudioEncoder> new_encoder) {
     ModifyEncoder([&](std::unique_ptr<AudioEncoder>* encoder) {