unittest step2: bye bye to multiple entrypoints for unittest

client/tests/client/dom/StorageTest.dart

 #library('StorageTest');
-#import('../../../../lib/unittest/unittest_dom.dart');
+#import('../../../../lib/unittest/unittest.dart');
+#import('../../../../lib/unittest/dom_config.dart');
 #import('dart:dom');
 
 main() {
-  forLayoutTests();
+  useDomConfiguration(isLayoutTest: true);
   test('GetItem', () {
     final value = window.localStorage.getItem('does not exist');
     Expect.isNull(value);
   });
   test('SetItem', () {
     final key = 'foo';
     final value = 'bar';
     window.localStorage.setItem(key, value);
     final stored = window.localStorage.getItem(key);
     Expect.equals(value, stored);
   });
 }