Smooth BWE and pass it to Audio Network Adaptor.

webrtc/common_audio/smoothing_filter.h

Index: webrtc/common_audio/smoothing_filter.h
diff --git a/webrtc/common_audio/smoothing_filter.h b/webrtc/common_audio/smoothing_filter.h
index 64a83d14848ae6200edefd4a6d6e271feac12242..03eb718d54f05c3c2df7d30ae5984a4ef2443ae8 100644
--- a/webrtc/common_audio/smoothing_filter.h
+++ b/webrtc/common_audio/smoothing_filter.h
@@ -23,6 +23,7 @@ class SmoothingFilter {
   virtual ~SmoothingFilter() = default;
   virtual void AddSample(float sample) = 0;
   virtual rtc::Optional<float> GetAverage() const = 0;
+  virtual void SetTimeConstantMs(int time_constant_ms) = 0;
 };
 
 // SmoothingFilterImpl applies an exponential filter
@@ -35,9 +36,10 @@ class SmoothingFilterImpl final : public SmoothingFilter {
 
   void AddSample(float sample) override;
   rtc::Optional<float> GetAverage() const override;
+  void SetTimeConstantMs(int time_constant_ms) override;
 
  private:
-  const int time_constant_ms_;
+  int time_constant_ms_;
   const Clock* const clock_;
 
   bool first_sample_received_;