Bug 1978428 - part1 : implement MediaKeySessionClosedReason and return closed-by-application for closed. r=media-playback-reviewers,webidl,padenot,emilio

The default is returning `closed-by-application` for `closed` per the spec [1]. We
will implement returning other reasons in bug 1978434.

[1] https://w3c.github.io/encrypted-media/#ref-for-dom-mediakeysessionclosedreason-closed-by-application-3

Differential Revision: https://phabricator.services.mozilla.com/D258313

Author: alastor0325

dom/media/eme/MediaKeySession.cpp

@@ -518,7 +518,7 @@ void MediaKeySession::OnClosed() {
   mIsClosed = true;
   mKeys->OnSessionClosed(this);
   mKeys = nullptr;
-  mClosed->MaybeResolveWithUndefined();
+  mClosed->MaybeResolve(MediaKeySessionClosedReason::Closed_by_application);
 }
 
 bool MediaKeySession::IsClosed() const { return mIsClosed; }

dom/webidl/MediaKeySession.webidl

@@ -10,6 +10,14 @@
  * W3C liability, trademark and document use rules apply.
  */
 
+enum MediaKeySessionClosedReason {
+  "internal-error",
+  "closed-by-application",
+  "release-acknowledged",
+  "hardware-context-reset",
+  "resource-evicted"
+};
+
 [Exposed=Window]
 interface MediaKeySession : EventTarget {
   // error state
@@ -20,7 +28,7 @@ interface MediaKeySession : EventTarget {
 
   readonly attribute unrestricted double expiration;
 
-  readonly attribute Promise<undefined> closed;
+  readonly attribute Promise<MediaKeySessionClosedReason> closed;
 
   readonly attribute MediaKeyStatusMap keyStatuses;