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.

lib/OpenLayers/Tile/Image.js

@@ -379,17 +379,9 @@ OpenLayers.Tile.Image = OpenLayers.Class(OpenLayers.Tile, {
     onImageLoad: function() {
         var img = this.imgDiv;
         OpenLayers.Event.stopObservingElement(img);
-
+        img.style.visibility = 'inherit';
-        OpenLayers.Animation.requestFrame(OpenLayers.Function.bind(function() {
+        img.style.opacity = this.layer.opacity;
-            // make sure we are not destroyed and not being reused for a
+        this.events.triggerEvent("loadend");
-            // different image
-            if (this.imgDiv === img) {
-                img.style.visibility = 'inherit';
-                img.style.opacity = this.layer.opacity;
-                this.events.triggerEvent("loadend");
-            }
-        }, this));
-
         this.isLoading = false;
         this.canvasContext = null;
 

tests/Layer/Grid.html

@@ -770,9 +770,6 @@
     }
 
     function test_setOpacity(t) {
-        var origRequestFrame = OpenLayers.Animation.requestFrame;
-        OpenLayers.Animation.requestFrame = function(fn) { fn(); };
-        
         t.plan(5);
 
         var map = new OpenLayers.Map('map');
@@ -801,8 +798,6 @@
         t.eq(parseFloat(tile.imgDiv.style.opacity), 0.2, "tile opacity is correc");
 
         map.destroy();
-        
-        OpenLayers.Animation.requestFrame = origRequestFrame
     }
     
     function test_getServerResolution(t) {
@@ -1313,9 +1308,6 @@
     }
 
     function test_delayed_back_buffer_removal(t) {
-        var origRequestFrame = OpenLayers.Animation.requestFrame;
-        OpenLayers.Animation.requestFrame = function(fn) { fn(); };
-
         //
         // Test that the delaying of the back buffer removal behaves
         // as expected.
@@ -1359,8 +1351,6 @@
         // tear down
 
         map.destroy();
-        
-        OpenLayers.Animation.requestFrame = origRequestFrame;
     }
     
     function test_getGridData(t) {

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;