Drive SVG Animations via requestAnimationFrame

LayoutTests/svg/animations/mozilla/animateMotion-mpath-pathLength-1.svg

 <svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" onload="loaded()">
   <defs>
     <path id="path" pathLength="100" d="M-200,0 h400" />
   </defs>
   <rect width="100%" height="100%" fill="lime"/>
 
   <!-- calcMode="linear" -->
   <rect x="10" y="10" width="100" height="100" fill="red"/>
   <rect x="10" y="10" width="100" height="100" fill="lime">
     <animateMotion dur="1s" keyPoints="0;1" keyTimes="0;1" calcMode="linear">
       <mpath xlink:href="#path" />
     </animateMotion>
   </rect>
 
   <!-- calcMode="paced" -->
   <rect x="10" y="110" width="100" height="100" fill="red"/>
   <rect x="10" y="110" width="100" height="100" fill="lime">
     <animateMotion dur="1s">
       <mpath xlink:href="#path" />
     </animateMotion>
   </rect>
 
 <script>
 if (window.testRunner)
     testRunner.waitUntilDone();
 
 function loaded() {
+    document.documentElement.pauseAnimations();
     document.documentElement.setCurrentTime(0.5);
     if (window.testRunner)
         testRunner.notifyDone();
 }
 </script>
 </svg>