Removing setImmediate and hiding WindowTimers interface (take 2)

tests/html/microtask_test.dart

-// Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
-// for details. All rights reserved. Use of this source code is governed by a
-// BSD-style license that can be found in the LICENSE file.
-
-library microtask_;
-import '../../pkg/unittest/lib/unittest.dart';
-import '../../pkg/unittest/lib/html_config.dart';
-import 'dart:async';
-import 'dart:html';
-
-main() {
-  useHtmlConfiguration();
-
-  test('setImmediate', () {
-    var timeoutCalled = false;
-    var rafCalled = false;
-    var immediateCalled = false;
-
-    Timer.run(expectAsync0(() {
-      timeoutCalled = true;
-      expect(immediateCalled, true);
-    }));
-
-
-    window.requestAnimationFrame((_) {
-      rafCalled = true;
-    });
-
-    window.setImmediate(expectAsync0(() {
-      expect(timeoutCalled, false);
-      expect(rafCalled, false);
-      immediateCalled = true;
-    }));
-    expect(immediateCalled, false);
-  });
-}