Refactor of various layout tests to use RAF

LayoutTests/svg/custom/js-late-gradient-creation.svg

 <?xml version="1.0" encoding="UTF-8"?>
 <!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1 Basic//EN" "http://www.w3.org/Graphics/SVG/1.1/DTD/svg11-basic.dtd">  
 <svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" id="svg-root" width="100%" height="100%" viewBox="0 0 480 360" onload="runRepaintAndPixelTest()">
 <script xlink:href="../../fast/repaint/resources/text-based-repaint.js"/>
 <g id="content" transform="scale(1, 1.5)">
      <text font-size="68" fill="url(#dynGrad)"  x="20" y="70">Gradient on fill</text>
 </g>
 <script>
     window.testIsAsync = true;
     var content = document.getElementById("content");
 
     function repaintTest() {
-        setTimeout(createGradient, 0);
+        requestAnimationFrame(createGradient);
     }
 
     function createGradient()
     {
         var gradient = document.createElementNS("http://www.w3.org/2000/svg", "linearGradient");
         gradient.setAttribute("id", "dynGrad");
         gradient.setAttribute("x1", "0");
         gradient.setAttribute("x2", "1");
 
         var stop1 = document.createElementNS("http://www.w3.org/2000/svg", "stop");
         stop1.setAttribute("stop-color", "blue");
         stop1.setAttribute("offset", "0");
 
         var stop2 = document.createElementNS("http://www.w3.org/2000/svg", "stop");
         stop2.setAttribute("stop-color", "red");
         stop2.setAttribute("offset", "1");
 
         gradient.appendChild(stop1);
         gradient.appendChild(stop2);
 
         content.appendChild(gradient);
 
         finishRepaintTest();
     }
 </script>
 
 </svg>