Smooth BWE and pass it to Audio Network Adaptor.

webrtc/common_audio/smoothing_filter.cc

Index: webrtc/common_audio/smoothing_filter.cc
diff --git a/webrtc/common_audio/smoothing_filter.cc b/webrtc/common_audio/smoothing_filter.cc
index 1cf9580d2adfeea7821b36e759651b8b2cd58281..ff79ab8799e9de332ff324152e97c43947837e6a 100644
--- a/webrtc/common_audio/smoothing_filter.cc
+++ b/webrtc/common_audio/smoothing_filter.cc
@@ -59,4 +59,9 @@ rtc::Optional<float> SmoothingFilterImpl::GetAverage() const {
                                                   : rtc::Optional<float>(value);
 }
 
+void SmoothingFilterImpl::SetTimeConstantMs(int time_constant_ms) {
+  time_constant_ms_ = time_constant_ms;
+  filter_.UpdateBase(exp(1.0f / time_constant_ms_));
+}
+
 }  // namespace webrtc