Attempting to de-flake async_window test.

tests/html/async_window_test.dart

 library AsyncWindowTest;
 import '../../pkg/unittest/lib/unittest.dart';
 import '../../pkg/unittest/lib/html_config.dart';
 import 'dart:html';
 
 main() {
   useHtmlConfiguration();
   test('Window.setTimeout', () {
     window.setTimeout(expectAsync0((){}), 10);
   });
   test('Window.setInterval', () {
     int counter = 0;
     int id = null;
-    id = window.setInterval(expectAsync0(() {
-      if (counter == 3) {
-        counter = 1024;
-        window.clearInterval(id);
-        // Wait some more time to be sure callback won't be invoked any more.
-        window.setTimeout(expectAsync0((){}), 50);
-        return;
-      }
-      // As callback should have been cleared on 4th invocation, counter
-      // should never be greater than 3.
-      assert(counter < 3);
-      counter++;
-    }, 3), 10);
+    id = window.setInterval(expectAsyncUntil0(
+      () {
+        if (counter == 3) {
+          counter = 1024;
+          window.clearInterval(id);
+          // Wait some more time to be sure callback won't be invoked any more.
+          window.setTimeout(expectAsync0((){}), 50);
+          return;
+        }
+        // As callback should have been cleared on 4th invocation, counter
+        // should never be greater than 3.
+        assert(counter < 3);
+        counter++;
+      },
+      () => counter == 3), 10);
   });
 }