Fix race condition bug in MediaSourceDuration test on 2018 and tip. A duration change could happen while audio source buffers are still appending.

Change-Id: I0a8e3d9bd93779e78f5c0dc69b3e330c991ed15f

js/tests/2018/conformanceTest.js

@@ -1253,9 +1253,12 @@ var createMediaSourceDurationTest = function(videoStream, audioStream) {
 
     var audioXhr = runner.XHRManager.createRequest(audioStream.src,
         function(e) {
+      audioSb.addEventListener('updateend', function onAudioUpdate() {
+        audioSb.removeEventListener('updateend', onAudioUpdate);
+        appendVideo();
+      });
       var audioContent = audioXhr.getResponseData();
       audioSb.appendBuffer(audioContent);
-      appendVideo();
     });
     audioXhr.send();
   };

js/tests/tip/conformanceTest.js

@@ -1253,9 +1253,12 @@ var createMediaSourceDurationTest = function(videoStream, audioStream) {
 
     var audioXhr = runner.XHRManager.createRequest(audioStream.src,
         function(e) {
+      audioSb.addEventListener('updateend', function onAudioUpdate() {
+        audioSb.removeEventListener('updateend', onAudioUpdate);
+        appendVideo();
+      });
       var audioContent = audioXhr.getResponseData();
       audioSb.appendBuffer(audioContent);
-      appendVideo();
     });
     audioXhr.send();
   };