Bug 1343459. Part 2 - remove the 'updateend' handler which might fire…

… before we register it. r=jya

Note the race is uncovered by P1 which kinda change the order of events.

MozReview-Commit-ID: 3INYvJVUhSG

--HG--
extra : rebase_source : e378c2a437a5a729008d39570be2a9087a7eb5f7
extra : intermediate-source : 02e2ecfea068dd9f487791287064e684a15dd599
extra : source : f2f40c70a2304e3e499422f3a7c46b59b54ad1ae

dom/media/mediasource/test/test_AudioChange_mp4.html

@@ -53,11 +53,8 @@
     })
     .then(fetchAndLoad.bind(null, audiosb, 'aac51-48000-128000-', ['2'], '.m4s'))
     .then(function() {
-      var promises = [];
       ms.endOfStream();
-      promises.push(once(el, 'ended'));
-      promises.push(once(audiosb, 'updateend'));
-      return Promise.all(promises);
+      return once(el, 'ended');
     })
     .then(function() {
       ok(el.currentTime >= 6, "played to the end");