Bug 1582569 - part2 : modify tests. r=chunmin

Differential Revision: https://phabricator.services.mozilla.com/D82580

dom/media/mediasession/test/MediaSessionTestUtils.js

@@ -5,6 +5,7 @@ const gMediaSessionActions = [
   "seekforward",
   "previoustrack",
   "nexttrack",
+  "skipad",
   "stop",
 ];
 

dom/media/mediasession/test/test_setactionhandler.html

@@ -17,6 +17,7 @@ const ACTIONS = [
   "seekforward",
   "previoustrack",
   "nexttrack",
+  "skipad",
   "stop",
 ];
 

testing/web-platform/tests/mediasession/setactionhandler.html

@@ -13,6 +13,7 @@ test(function(t) {
   window.navigator.mediaSession.setActionHandler("seekforward", null);
   window.navigator.mediaSession.setActionHandler("stop", null);
   window.navigator.mediaSession.setActionHandler("seekto", null);
+  window.navigator.mediaSession.setActionHandler("skipad", null);
 }, "Test that setActionHandler() can be executed for supported actions");
 
 test(function(t) {