Not using requestAnimationFrame

Using the Timeline tab of the Chrome Developer Tools, no significant
difference of Paint events can be observed when requestAnimationFrame is
used. So I agree with @elemoine that there is no need to introduce
asynchronous behavior here.

tests/Tile/Image.html

@@ -4,8 +4,6 @@
   <script type="text/javascript">
     // turn off tile queue, so we can check img urls in tests
     delete OpenLayers.Layer.Grid.prototype.queueTileDraw;
-    // turn off animation, so we don't need to test asynchronously
-    OpenLayers.Animation.requestFrame = function(fn) { fn(); };
 
     var isMozilla = (navigator.userAgent.indexOf("compatible") == -1);
     var tile;