Corrected the behavior in AEC3 during buffer overruns and underruns

webrtc/modules/audio_processing/aec3/shadow_filter_update_gain.h

Index: webrtc/modules/audio_processing/aec3/shadow_filter_update_gain.h
diff --git a/webrtc/modules/audio_processing/aec3/shadow_filter_update_gain.h b/webrtc/modules/audio_processing/aec3/shadow_filter_update_gain.h
index a67b8fb63694ab8d46685785893c3415a6c64b9a..72218b6608878e28ed2901069c6d9f8a42522d4c 100644
--- a/webrtc/modules/audio_processing/aec3/shadow_filter_update_gain.h
+++ b/webrtc/modules/audio_processing/aec3/shadow_filter_update_gain.h
@@ -21,6 +21,9 @@ namespace webrtc {
 // Provides functionality for computing the fixed gain for the shadow filter.
 class ShadowFilterUpdateGain {
  public:
+  // Takes action in the case of a known echo path change.
+  void HandleEchoPathChange();
+
   // Computes the gain.
   void Compute(const RenderBuffer& render_buffer,
                const RenderSignalAnalyzer& render_signal_analyzer,
@@ -30,6 +33,8 @@ class ShadowFilterUpdateGain {
                FftData* G);
 
  private:
+  // TODO(peah): Check whether this counter should instead be initialized to a
+  // large value.
   size_t poor_signal_excitation_counter_ = 0;
   size_t call_counter_ = 0;
 };