Make event_order_loadstart_progress.htm deterministic (fixes servo/servo#18289)

tests/wpt/metadata/MANIFEST.json

@@ -569381,7 +569381,7 @@
    "testharness"
   ],
   "html/semantics/embedded-content/media-elements/event_order_loadstart_progress.html": [
-   "013746f8434b90d53724e7cd924f8b430cdc52b3",
+   "1a22967566471d711f6b82c8e59ebd6b8681b004",
    "testharness"
   ],
   "html/semantics/embedded-content/media-elements/event_pause.html": [

tests/wpt/metadata/html/semantics/embedded-content/media-elements/event_order_loadstart_progress.html.ini

@@ -1,6 +1,5 @@
 [event_order_loadstart_progress.html]
   type: testharness
-  expected: TIMEOUT
   [setting src attribute on autoplay audio should trigger loadstart then progress event]
-    expected: NOTRUN
+    expected: FAIL
 

tests/wpt/web-platform-tests/html/semantics/embedded-content/media-elements/event_order_loadstart_progress.html

@@ -14,39 +14,37 @@
   </video>
   <div id="log"></div>
   <script>
-test(function() {
+(function() {
   var t = async_test("setting src attribute on autoplay audio should trigger loadstart then progress event", {timeout:5000});
   var a = document.getElementById("a");
   var found_loadstart = false;
-  a.addEventListener("loadstart", function() {
+  a.addEventListener("error", t.unreached_func());
+  a.addEventListener("loadstart", t.step_func(function() {
     found_loadstart = true;
-  });
+  }));
-  a.addEventListener("progress", function() {
+  a.addEventListener("progress", t.step_func(function() {
-    t.step(function() {
+    assert_true(found_loadstart);
-     assert_true(found_loadstart);
-    });
     t.done();
     a.pause();
-  }, false);
+  }), false);
   a.src = getAudioURI("/media/sound_5") + "?" + new Date() + Math.random();
-}, "audio events - loadstart, then progress");
+})();
 
-test(function() {
+(function() {
   var t = async_test("setting src attribute on autoplay video should trigger loadstart then progress event", {timeout:5000});
   var v = document.getElementById("v");
   var found_loadstart = false;
-  v.addEventListener("loadstart", function() {
+  v.addEventListener("error", t.unreached_func());
+  v.addEventListener("loadstart", t.step_func(function() {
     found_loadstart = true;
-  });
+  }));
-  v.addEventListener("progress", function() {
+  v.addEventListener("progress", t.step_func(function() {
-    t.step(function() {
+    assert_true(found_loadstart);
-     assert_true(found_loadstart);
-    });
     t.done();
     v.pause();
-  }, false);
+  }), false);
   v.src = getVideoURI("/media/movie_5") + "?" + new Date() + Math.random();
-}, "video events - loadstart, then progress");
+})();
   </script>
  </body>
 </html>