Bug 1678373 - Don't detach the media element from the tree for checking play time probes: it pauses the media element per spec. r=alwu

Differential Revision: https://phabricator.services.mozilla.com/D125080

dom/media/test/chrome/test_accumulated_play_time.html

@@ -87,7 +87,8 @@ add_task(async function testVisiblePlayTime() {
   assertValueKeptUnchanged(videoChrome, "invisiblePlayTime");
 
   info(`make video invisible`);
-  document.body.removeChild(video);
+  video.style.display = "none";
+  await once(video, "mozinvisibleplaytimestarted");
   await assertValueConstantlyIncreases(videoChrome, "totalPlayTime");
   await assertValueConstantlyIncreases(videoChrome, "invisiblePlayTime");
   assertValueKeptUnchanged(videoChrome, "visiblePlayTime");