Update unittest to new package layout.

utils/tests/pub/lock_file_test.dart

 // Copyright (c) 2012, 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('lock_file_test');
 
-#import('../../../pkg/unittest/unittest.dart');
+#import('../../../pkg/unittest/lib/unittest.dart');
 #import('../../pub/lock_file.dart');
 #import('../../pub/package.dart');
 #import('../../pub/source.dart');
 #import('../../pub/source_registry.dart');
 #import('../../pub/utils.dart');
 #import('../../pub/version.dart');
 #import('../../pub/yaml/yaml.dart');
 
 class MockSource extends Source {
   final String name = 'mock';
@@ skipping 168 matching lines @@
               'version': '3.2.1',
               'source': 'mock',
               'description': 'bar desc'
             }
           }
         }));
       });
     });
   });
 }