Reverting setTimeout removal.

tests/html/async_window_test.dart

 library AsyncWindowTest;
 import '../../pkg/unittest/lib/unittest.dart';
 import '../../pkg/unittest/lib/html_config.dart';
 import 'dart:html';
-import 'dart:async';
 
 main() {
   useHtmlConfiguration();
-  test('Timer', () {
-    new Timer(const Duration(milliseconds: 10), expectAsync0((){}));
+  test('Window.setTimeout', () {
+    window.setTimeout(expectAsync0((){}), 10);
   });
-  test('Timer.repeating', () {
+  test('Window.setInterval', () {
     int counter = 0;
     int id = null;
-    new Timer.repeating(const Duration(milliseconds: 10),
-        expectAsyncUntil1(
-        (timer) {
-          if (counter == 3) {
-            counter = 1024;
-            timer.cancel();
-            // Wait some more time to be sure callback won't be invoked any
-            // more.
-            new Timer(const Duration(milliseconds: 50), expectAsync0((){}));
-            return;
-          }
-          // As callback should have been cleared on 4th invocation, counter
-          // should never be greater than 3.
-          assert(counter < 3);
-          counter++;
-        },
-        () => counter == 3));
+    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);
   });
 }