Replace AudioSilenceDetector with an AudioPowerMonitor.

content/public/browser/media_observer.h

Index: content/public/browser/media_observer.h
diff --git a/content/public/browser/media_observer.h b/content/public/browser/media_observer.h
index 65c97054f41e5cfa64da82060f1c75a870bd1a23..fcaa6e7886026ae1582ba0a004de8a58ddc10bf7 100644
--- a/content/public/browser/media_observer.h
+++ b/content/public/browser/media_observer.h
@@ -29,13 +29,15 @@ class MediaObserver {
       const MediaStreamDevice& device,
       MediaRequestState state) = 0;
 
-  // Called when an audio stream transitions into playing audible or silent
-  // sound, and when the stream is stopped.
+  // Called when an audio stream transitions into a playing or paused state, and
+  // also at regular intervals to report the current power level of the audio
+  // signal in dBFS (decibels relative to full-scale) units.
   virtual void OnAudioStreamPlayingChanged(
       int render_process_id,
       int render_view_id,
       int stream_id,
-      bool is_playing_and_audible) = 0;
+      bool is_playing,
+      float power_level_dbfs) = 0;
 
  protected:
   virtual ~MediaObserver() {}