Copy lib/dom tests that use dart:html to lib/html.

tests/dom/async_window_test.dart

-#library('AsyncWindowTest');
-#import('../../lib/unittest/unittest.dart');
-#import('../../lib/unittest/html_config.dart');
-#import('dart:html');
-
-main() {
-  useHtmlConfiguration();
-  asyncTest('Window.setTimeout', 1, () {
-    window.setTimeout(callbackDone, 10);
-  });
-  asyncTest('Window.setInterval', 1, () {
-    int counter = 0;
-    int id = null;
-    id = window.setInterval(() {
-      if (counter == 3) {
-        counter = 1024;
-        window.clearInterval(id);
-        // Wait some more time to be sure callback won't be invoked any more.
-        window.setTimeout(callbackDone, 50);
-        return;
-      }
-      // As callback should have been cleared on 4th invocation, counter
-      // should never be greater than 3.
-      assert(counter < 3);
-      counter++;
-    }, 10);
-  });
-}