Add vector_math::FMUL. Replace audio_util::AdjustVolume.

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 9d9563c1d27864c50c7dd0f7eb32c38ee4878278..61a53ed028606f3892975b973c5a471a890ead6d 100644
--- a/media/base/audio_bus.h
+++ b/media/base/audio_bus.h
@@ -92,6 +92,10 @@ class MEDIA_EXPORT AudioBus {
   void ZeroFrames(int frames);
   void ZeroFramesPartial(int start_frame, int frames);
 
+  // Scale internal channel values by |volume| >= 0.  If an invalid value
+  // is provided, no adjustment is done.
+  void Scale(float volume);
+
  private:
   friend struct base::DefaultDeleter<AudioBus>;
   ~AudioBus();