anchor.diff:  
     SoundEffectStream play(
       SoundEffect sound,
  -    [Object tag,
  -      bool loop = false,
  +    [bool loop = false,
         double volume = 1.0,
         double pitch = 1.0,
         double pan = 0.0,
  
positive.code:   double volume = 1.0;
    double pitch = 1.0;
    double pan = 0.0;
    Object tag;
  
    // TODO: Implement completion callback. On completion, sounds should
    // also be removed from the list of playing sounds.
  
negative.code:         playingSound._player.ptr.start();
        });
  
        _soundEffectStreams.add(playingSound);
        _mediaPlayers[sound] = playingSound._player;
      } else {
        // Reuse player
  