Remove unnecessary casts in AudioManagerDeleter on Mac.

media/audio/audio_manager.h

Index: media/audio/audio_manager.h
diff --git a/media/audio/audio_manager.h b/media/audio/audio_manager.h
index c5a7cdd949b96f912b1ca50aca03da4439bae293..2826bcd7dba5e2b13cb350415f1280abd5fdcc62 100644
--- a/media/audio/audio_manager.h
+++ b/media/audio/audio_manager.h
@@ -261,6 +261,7 @@ class MEDIA_EXPORT AudioManager {
 
  private:
   friend class base::DeleteHelper<AudioManager>;
+  friend class AudioManagerDeleter;
 
   scoped_refptr<base::SingleThreadTaskRunner> task_runner_;
   scoped_refptr<base::SingleThreadTaskRunner> worker_task_runner_;