Add a silent audio sink to consume WebAudio data on silence detection.

media/base/audio_bus.h

Index: media/base/audio_bus.h
diff --git a/media/base/audio_bus.h b/media/base/audio_bus.h
index 25e2839697a9ba1f639f7268fc05bb8395ae602c..cf598c2a5c939d5d7369b25e0abe73aefd48d22f 100644
--- a/media/base/audio_bus.h
+++ b/media/base/audio_bus.h
@@ -101,6 +101,9 @@ class MEDIA_EXPORT AudioBus {
   void ZeroFrames(int frames);
   void ZeroFramesPartial(int start_frame, int frames);
 
+  // Checks if all frames are zero.
+  bool AreFramesZero() const;
+
   // Scale internal channel values by |volume| >= 0.  If an invalid value
   // is provided, no adjustment is done.
   void Scale(float volume);