Deflake video-overlay-menu.html

This CL uses video.requestVideoFrameCallback to make sure a frame is
displayed before ending the test. It's possible this test might
still flake if the overflow menu doesn't show up on screen in time.

Bug: 1145491
Change-Id: Ic402b396cf49d9c2e6853a039e44f739bb2cc014
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2567571
Commit-Queue: Mounir Lamouri <mlamouri@chromium.org>
Auto-Submit: Thomas Guilbert <tguilbert@chromium.org>
Reviewed-by: Mounir Lamouri <mlamouri@chromium.org>
Cr-Commit-Position: refs/heads/master@{#832620}

third_party/blink/web_tests/fast/forms/color-scheme/media/video-overlay-menu.html

@@ -9,13 +9,12 @@
     <video controls></video>
     <script>
         var video = document.querySelector("video");
-        video.src = "../../../../media/content/test.ogv";
         enableTestMode(video);
-        init();
         video.onloadeddata = function () {
             var overflowMenu = getOverflowMenuButton(video);
             var coords = elementCoordinates(overflowMenu);
             clickAtCoordinates(coords[0], coords[1]);
         };
+        setVideoSrcAndWaitForFirstFrame("../../../../media/content/test.ogv");
     </script>
-</body>
+</body>
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