Move unittest from lib to pkg.

tests/html/element_classes_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('ElementTest');
-#import('../../lib/unittest/unittest.dart');
-#import('../../lib/unittest/html_config.dart');
+#import('../../pkg/unittest/unittest.dart');
+#import('../../pkg/unittest/html_config.dart');
 #import('dart:html');
 
 main() {
   useHtmlConfiguration();
 
   Element makeElement() => new Element.tag('div');
 
   Element makeElementWithChildren() =>
     new Element.html("<div><br/><img/><input/></div>");
 
@@ skipping 135 matching lines @@
     Expect.setEquals(['foo', 'baz'],
         classes.intersection(['foo', 'qux', 'baz']));
   });
 
   test('clear', () {
     final classes = makeClassSet();
     classes.clear();
     Expect.setEquals([], classes);
   });
 }