pkg/unittest: config refactor

pkg/unittest/lib/html_individual_config.dart

Index: pkg/unittest/lib/html_individual_config.dart
diff --git a/pkg/unittest/lib/html_individual_config.dart b/pkg/unittest/lib/html_individual_config.dart
index 2432a55733c6f186df379a1082522b17ffe8ef71..a6bc60ee4147ac009b4dfc8239b5ee1f1505722b 100644
--- a/pkg/unittest/lib/html_individual_config.dart
+++ b/pkg/unittest/lib/html_individual_config.dart
@@ -1,4 +1,4 @@
-// Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
+// Copyright (c) 2013, 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.
 
@@ -43,6 +43,8 @@ class HtmlIndividualConfiguration extends htmlconfig.HtmlConfiguration {
 }
 
 void useHtmlIndividualConfiguration([bool isLayoutTest = false]) {
-  if (unittest.config != null) return;
-  unittest.configure(new HtmlIndividualConfiguration(isLayoutTest));
+  unittest.config = isLayoutTest ? _singletonLayout : _singletonNotLayout;
 }
+
+final _singletonLayout = new HtmlIndividualConfiguration(true);
+final _singletonNotLayout = new HtmlIndividualConfiguration(false);