[AudioStreamMonitor] Adds API to collect frame-level audibility.

content/public/browser/render_frame_host.h

Index: content/public/browser/render_frame_host.h
diff --git a/content/public/browser/render_frame_host.h b/content/public/browser/render_frame_host.h
index 49baa59a8392a7ccb6813f7eefa6efaa1d491158..9c9a428459addc7c1f92600169ab43db63a0798f 100644
--- a/content/public/browser/render_frame_host.h
+++ b/content/public/browser/render_frame_host.h
@@ -240,6 +240,10 @@ class CONTENT_EXPORT RenderFrameHost : public IPC::Listener,
   // Returns true if the frame has a selection.
   virtual bool HasSelection() = 0;
 
+  // Returns true if the frame recently plays an audio.
+  virtual bool IsAudible() = 0;
+  virtual void OnAudioStateChanged(bool audible) = 0;
+
   // Text surrounding selection.
   typedef base::Callback<
       void(const base::string16& content, int start_offset, int end_offset)>