Bug 1407650 - Avoid test_mr_record_changing_video_resolution.html by delaying stop(). r=jib

Differential Revision: https://phabricator.services.mozilla.com/D18050

--HG--
extra : moz-landing-system : lando

dom/media/test/test_mediarecorder_record_changing_video_resolution.html

@@ -144,7 +144,11 @@ function startTest() {
     previous_time = timestamp;
 
     if (countFrames == resolution_change.length) {
-      mediaRecorder.stop();
+      // There's a race between this stop() and feeding the last frame to the
+      // recorder, see bug 1407650. We wait a bit with the stop() as a stop-gap
+      // measure.
+      SimpleTest.requestFlakyTimeout("Fixes intermittent bug 1407650");
+      new Promise(r => setTimeout(r, 1000)).then(() => mediaRecorder.stop());
       return;
     }