Refactor Source and SourceRegistry.

lib/src/command/list_package_dirs.dart

 // Copyright (c) 2013, 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 'package:path/path.dart' as p;
 
 import '../command.dart';
 import '../io.dart';
 import '../log.dart' as log;
 import '../utils.dart';
@@ skipping 16 matching lines @@
     log.json.enabled = true;
 
     if (!fileExists(entrypoint.lockFilePath)) {
       dataError('Package "myapp" has no lockfile. Please run "pub get" first.');
     }
 
     var output = {};
 
     // Include the local paths to all locked packages.
     var packages = mapMap(entrypoint.lockFile.packages, value: (name, package) {
-      var source = entrypoint.cache.sources[package.source];
+      var source = entrypoint.cache.source(package.source);
       var packageDir = source.getDirectory(package);
       // Normalize paths and make them absolute for backwards compatibility
       // with the protocol used by the analyzer.
       return p.normalize(p.absolute(p.join(packageDir, "lib")));
     });
 
     // Include the self link.
     packages[entrypoint.root.name] =
         p.normalize(p.absolute(entrypoint.root.path("lib")));
 
     output["packages"] = packages;
 
     // Include the file(s) which when modified will affect the results. For pub,
     // that's just the pubspec and lockfile.
     output["input_files"] = [
       p.normalize(p.absolute(entrypoint.lockFilePath)),
       p.normalize(p.absolute(entrypoint.pubspecPath))
     ];
 
     log.json.message(output);
   }
 }