Bug 1654045 - part3 : porting other attributes to media controller's webidl interface. r=chunmin

We have already had these functions on `MediaController` so we just need to expose them on the media controller's webidl interface, and they can be used in testing and the future plan of supporting media hub.

Differential Revision: https://phabricator.services.mozilla.com/D85230

dom/chrome-webidl/MediaController.webidl

@@ -27,7 +27,10 @@ enum MediaControlKey {
  */
 [Exposed=Window, ChromeOnly]
 interface MediaController : EventTarget {
+  readonly attribute unsigned long long id;
   readonly attribute boolean isActive;
+  readonly attribute boolean isAudible;
+  readonly attribute boolean isPlaying;
 
   [Frozen, Cached, Pure]
   readonly attribute sequence<MediaControlKey> supportedKeys;