Add TODOs to convert from video-test.js to testharness.js

third_party/WebKit/LayoutTests/media/video-append-source.html

 <video controls></video>
 <script src=media-file.js></script>
+<!-- TODO(philipj): Convert test to testharness.js. crbug.com/588956
+     (Please avoid writing new tests using video-test.js) -->
 <script src=video-test.js></script>
 
 <script>
     testExpected("video.currentSrc", "");
     var mediaFile = findMediaFile("video", "content/test");
     var source = document.createElement("source");
     source.setAttribute("src", mediaFile);
     video.appendChild(source);
 
     testExpected("video.currentSrc", "");
 
     waitForEvent("canplaythrough", function () {
         testExpected("stripExtension(relativeURL(video.currentSrc))", stripExtension(mediaFile));
         endTest();
     });
 
 </script>