Fix XMLHttpRequest leak document when send() is called multiple times.

LayoutTests/fast/js/resources/leak-check.js

 // include fast/js/resources/js-test-pre.js before this file.
 
 function doLeakTest(src, tolerance) {
     function getCounterValues() {
         testRunner.resetTestHelperControllers();
         gc();
         return {'numberOfLiveDocuments': window.internals.numberOfLiveDocuments()};
     }
 
     var frame = document.createElement('iframe');
@@ skipping 32 matching lines @@
     loadSourceIntoIframe('about:blank', function() {
         // blank document loaded...
         var countersBefore = getCounterValues();
 
         loadSourceIntoIframe(src, function() {
             // target document loaded...
 
             loadSourceIntoIframe('about:blank', function() {
                 // target document unloaded...
 
-                var countersAfter = getCounterValues();
-                compareValues(countersBefore, countersAfter, tolerance);
-                finishJSTest();
+                // Measure counter values on next timer event. This is needed
+                // to correctly handle deref cycles for some ActiveDOMObjects
+                // such as XMLHttpRequest.
+                setTimeout(function() {
+                    var countersAfter = getCounterValues();
+                    compareValues(countersBefore, countersAfter, tolerance);
+                    finishJSTest();
+                }, 100);
             });
         });
     });
 }
 
 function htmlToUrl(html) {
     return 'data:text/html;charset=utf-8,' + html;
 }
 
 function grabScriptText(id) {
     return document.getElementById(id).innerText;
 }
 
 // include fast/js/resources/js-test-post.js after this file.