Make Source.getDirectory synchronous.

test/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 'dart:async';
 
 import 'package:pub/src/lock_file.dart';
 import 'package:pub/src/package.dart';
 import 'package:pub/src/pubspec.dart';
 import 'package:pub/src/source.dart';
 import 'package:pub/src/source_registry.dart';
 import 'package:pub_semver/pub_semver.dart';
 import 'package:test/test.dart';
 import 'package:yaml/yaml.dart';
 
 import 'test_pub.dart';
 
 class MockSource extends Source {
   final String name = 'mock';
 
   Future<Pubspec> doDescribe(PackageId id) => throw new UnsupportedError(
       "Cannot describe mock packages.");
 
   Future get(PackageId id, String symlink) => throw new UnsupportedError(
       "Cannot get a mock package.");
 
-  Future<String> getDirectory(PackageId id) => throw new UnsupportedError(
+  String getDirectory(PackageId id) => throw new UnsupportedError(
       "Cannot get the directory for mock packages.");
 
   dynamic parseDescription(String filePath, String description,
                            {bool fromLockFile: false}) {
     if (!description.endsWith(' desc')) throw new FormatException();
     return description;
   }
 
   bool descriptionsEqual(description1, description2) =>
       description1 == description2;
@@ skipping 178 matching lines @@
               'version': '3.2.1',
               'source': 'mock',
               'description': 'bar desc'
             }
           }
         }));
       });
     });
   });
 }