Restructure YAML package suitable for pub lish

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/lib/unittest.dart';
+import '../../../pkg/yaml/lib/yaml.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';
   final bool shouldCache = false;
 
   void validateDescription(String description, {bool fromLockFile: false}) {
     if (!description.endsWith(' desc')) throw new FormatException();
   }
 
   String packageName(String description) {
@@ skipping 149 matching lines @@
               'version': '3.2.1',
               'source': 'mock',
               'description': 'bar desc'
             }
           }
         }));
       });
     });
   });
 }