Post a microtask to load <img> elements.

LayoutTests/http/tests/security/cross-origin-createImageBitmap.html

Index: LayoutTests/http/tests/security/cross-origin-createImageBitmap.html
diff --git a/LayoutTests/http/tests/security/cross-origin-createImageBitmap.html b/LayoutTests/http/tests/security/cross-origin-createImageBitmap.html
index d8d31f04d2a53b8f5b239c28446279e60eccfd94..02416fd36f618e53b637aee5639e03cafdf16a01 100644
--- a/LayoutTests/http/tests/security/cross-origin-createImageBitmap.html
+++ b/LayoutTests/http/tests/security/cross-origin-createImageBitmap.html
@@ -8,19 +8,21 @@
         window.jsTestIsAsync = true;
 
         var img = document.createElement('img');
+        var vid = document.createElement('video');
+
         document.body.appendChild(img);
         img.src = 'http://localhost:8080/security/resources/abe.png';
-        
-        shouldThrow('createImageBitmap(img, 0, 0, 10, 10)', '"SecurityError: Failed to execute \'createImageBitmap\' on \'Window\': Cross-origin access to the source image is denied."');
+        img.addEventListener('load', function () {
+            shouldThrow('createImageBitmap(img, 0, 0, 10, 10)', '"SecurityError: Failed to execute \'createImageBitmap\' on \'Window\': Cross-origin access to the source image is denied."');
 
-        var vid = document.createElement('video');
-        vid.src = 'http://localhost:8080/media/resources/load-video.php?name=test.ogv&type=video/ogv';
-        vid.addEventListener('playing', function () {
-            shouldThrow('createImageBitmap(vid, 0, 0, 10, 10)', '"SecurityError: Failed to execute \'createImageBitmap\' on \'Window\': Cross-origin access to the source video is denied."');
-            finishJSTest();
+            vid.src = 'http://localhost:8080/media/resources/load-video.php?name=test.ogv&type=video/ogv';
+            vid.addEventListener('playing', function () {
+                shouldThrow('createImageBitmap(vid, 0, 0, 10, 10)', '"SecurityError: Failed to execute \'createImageBitmap\' on \'Window\': Cross-origin access to the source video is denied."');
+                finishJSTest();
+            });
+            document.body.appendChild(vid);
+            vid.play();
         });
-        document.body.appendChild(vid);
-        vid.play();
     </script>
 </body>
 </html>