Fix Document leak from NodeFilter.

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

+// include fast/js/resources/js-test-pre.js before this file.
+
+function doLeakTest(src, tolerance) {
+    function getCounterValues() {
+        gc();
+        return {'numberOfLiveDocuments': window.internals.numberOfLiveDocuments()};
+    }
+
+    var frame = document.createElement('frame');
+    document.body.appendChild(frame);
+    function loadSourceIntoIframe(src, callback) {
+        var originalSrc = frame.src;
+
+        frame.onload = function() {
+            if (frame.src === originalSrc)
+                return true;
+
+            callback();
+            return true;
+        };
+        frame.src = src;
+    }
+
+    function compareValues(countersBefore, countersAfter, tolerance) {
+        for (type in tolerance) {
+            var before = countersBefore[type];
+            var after = countersAfter[type];
+
+            if(after - before <= tolerance[type])
+                testPassed('The difference of counter "'+type+'" before and after the cycle is under the threshold of '+tolerance[type]+'.');
+            else
+                testFailed('counter "'+type+'" was '+before+' before and now '+after+' after the cycle. This exceeds the threshold of '+tolerance[type]+'.');
+        }
+    }
+
+    jsTestIsAsync = true;
+    if (!window.internals) {
+        debug("This test only runs on DumpRenderTree, as it requires existence of window.internals and cross-domain resource access check disabled.");
+        finishJSTest();
+    }
+
+    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();
+            });
+        });
+    });
+}
+
+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.