unittest step2: bye bye to multiple entrypoints for unittest

client/tests/client/dom/AsyncWindowTest.dart

 #library('AsyncWindowTest');
-#import('../../../../lib/unittest/unittest_dom.dart');
+#import('../../../../lib/unittest/unittest.dart');
+#import('../../../../lib/unittest/dom_config.dart');
 #import('dart:dom');
 
 main() {
-  forLayoutTests();
+  useDomConfiguration();
   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);
   });
 }