Expose media controls to accessibility

content/public/browser/media_session.h

Index: content/public/browser/media_session.h
diff --git a/content/public/browser/media_session.h b/content/public/browser/media_session.h
index 78a18898d4c8b414e6416a277d490781c9bf5057..509629f894ad72b8111d6e5a418046463e6d8c5b 100644
--- a/content/public/browser/media_session.h
+++ b/content/public/browser/media_session.h
@@ -55,6 +55,14 @@ class MediaSession {
   // Tell the media session a user action has performed.
   virtual void DidReceiveAction(blink::mojom::MediaSessionAction action) = 0;
 
+  // Let the media session start ducking such that the volume multiplier is
+  // reduced.
+  virtual void StartDucking() = 0;
+
+  // Let the media session stop ducking such that the volume multiplier is
+  // recovered.
+  virtual void StopDucking() = 0;
+
  protected:
   MediaSession() = default;
 };