Refactor Source and SourceRegistry.

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.
 
-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/src/system_cache.dart';
 import 'package:pub_semver/pub_semver.dart';
 import 'package:test/test.dart';
 import 'package:yaml/yaml.dart';
 
 class MockSource extends Source {
   final String name = 'mock';
 
-  Future<List<PackageId>> doGetVersions(PackageRef ref) =>
-      throw new UnsupportedError("Cannot get mock package versions.");
-
-  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.");
-
-  String getDirectory(PackageId id) => throw new UnsupportedError(
-      "Cannot get the directory for mock packages.");
+  BoundSource bind(SystemCache cache) =>
+      throw new UnsupportedError("Cannot download mock packages.");
 
   PackageRef parseRef(String name, description, {String containingPath}) {
     if (!description.endsWith(' desc')) throw new FormatException('Bad');
     return new PackageRef(name, this.name, description);
   }
 
   PackageId parseId(String name, Version version, description) {
     if (!description.endsWith(' desc')) throw new FormatException('Bad');
     return new PackageId(name, this.name, version, description);
   }
@@ skipping 177 matching lines @@
           'bar': {
             'version': '3.2.1',
             'source': 'mock',
             'description': 'bar desc'
           }
         }
       }));
     });
   });
 }