[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 db36975b359f33f3f9c83a0d6514e1a2f025edd8..a509708eeb31f48aad10e97421c13525f7603aab 100644
--- a/content/browser/frame_host/render_frame_host_impl.h
+++ b/content/browser/frame_host/render_frame_host_impl.h
@@ -182,6 +182,8 @@ class CONTENT_EXPORT RenderFrameHostImpl
   void FilesSelectedInChooser(const std::vector<FileChooserFileInfo>& files,
                               FileChooserParams::Mode permissions) override;
   bool HasSelection() override;
+  bool IsAudible() override;
+  void OnAudioStateChanged(bool audible) override;
   void RequestTextSurroundingSelection(
       const TextSurroundingSelectionCallback& callback,
       int max_length) override;
@@ -1182,6 +1184,9 @@ class CONTENT_EXPORT RenderFrameHostImpl
   // If true, then the RenderFrame has selected text.
   bool has_selection_;
 
+  // If true, then the RenderFrame is playing audio.
+  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.