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

third_party/WebKit/LayoutTests/media/video-src-invalid-poster.html

+<!-- 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>
 <video poster="content/abe.png">
     <source src="content/bogus" type="bogus">
 </video>
 <script>
     findMediaElement();
 
     function listenForWidthAndHeight(expectedWidth, expectedHeight, callback) {
         if (video.clientWidth == expectedWidth && video.clientHeight == expectedHeight) {
             callback();
         } else {
             // This uses a 20ms sleep loop to accomplish the wait, since the
             // standard specifies no events that fire on poster load or error.
             window.setTimeout(listenForWidthAndHeight, 20, expectedWidth, expectedHeight, callback);
         }
     }
 
     function expected() {
         testExpected("video.clientWidth", 76);
         testExpected("video.clientHeight", 103);
         endTest();
     }
 
     run("video.load()");
     waitForEvent("loadstart", function () {
         listenForWidthAndHeight(76, 103, expected);
     });
 </script>