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

content/browser/frame_host/render_frame_host_impl.h

Index: content/browser/frame_host/render_frame_host_impl.h
diff --git a/content/browser/frame_host/render_frame_host_impl.h b/content/browser/frame_host/render_frame_host_impl.h
index dc24b89172448e10974816d94a9411aae3f4351f..534b95d7fe08cb1193d903dd4dedd7869d6386a8 100644
--- a/content/browser/frame_host/render_frame_host_impl.h
+++ b/content/browser/frame_host/render_frame_host_impl.h
@@ -248,6 +248,10 @@ class CONTENT_EXPORT RenderFrameHostImpl
   // after they are blocked in RenderWidgetHelper::CreateNewWindow.
   void Init();
 
+  // Returns true if the frame recently plays an audio.
+  bool is_audible() const { return is_audible_; }
+  void OnAudioStateChanged(bool is_audible);

[miu, 2017/06/26 22:57:59]

naming nit: OnAudibleStateChanged

[lpy, 2017/06/28 02:14:29]

Done.

+
   int routing_id() const { return routing_id_; }
 
   // Called when this frame has added a child. This is a continuation of an IPC
@@ -1188,6 +1192,9 @@ class CONTENT_EXPORT RenderFrameHostImpl
   // If true, then the RenderFrame has selected text.
   bool has_selection_;
 
+  // If true, then the RenderFrame is playing audio.

[miu, 2017/06/26 22:57:59]

nit: Let's be a little more specific here, to help future developers that might
not be intimately familiar with this mechanism. It's important to distinguish
the difference between the existence of audio streams versus whether there are
audio streams present that are not silent. Suggestion:

  // If true, then this RenderFrame has one or more audio streams with audible
  // signal. If false, all audio streams are currently silent (or there are no
  // audio streams).

[lpy, 2017/06/28 02:14:29]

Done.

+  bool is_audible_;
+
   // PlzNavigate: The Previews state of the last navigation. This is used during
   // history navigation of subframes to ensure that subframes navigate with the
   // same Previews status as the top-level frame.