Media Session IDL tests

[Global=Window, Exposed=Global]
interface Window {
};

interface Navigator {
};

[Exposed=Window]
partial interface Navigator {
  [SameObject] readonly attribute MediaSession mediaSession;
};

enum MediaSessionPlaybackState {
  "none",
  "paused",
  "playing"
};

enum MediaSessionAction {
  "play",
  "pause",
  "seekbackward",
  "seekforward",
  "previoustrack",
  "nexttrack",
};

callback MediaSessionActionHandler = void();

[Exposed=Window]
interface MediaSession {
  attribute MediaMetadata? metadata;

  attribute MediaSessionPlaybackState playbackState;

  void setActionHandler(MediaSessionAction action, MediaSessionActionHandler? handler);
};

[Constructor(optional MediaMetadataInit init), Exposed=Window]
interface MediaMetadata {
  attribute DOMString title;
  attribute DOMString artist;
  attribute DOMString album;
  attribute FrozenArray artwork;
};

dictionary MediaMetadataInit {
  DOMString title = "";
  DOMString artist = "";
  DOMString album = "";
  sequence artwork = [];
};

dictionary MediaImage {
  required USVString src;
  DOMString sizes = "";
  DOMString type = "";
};