Refactor Source and SourceRegistry.

lib/src/command/cache_add.dart

 // Copyright (c) 2014, 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_semver/pub_semver.dart';
 
 import '../command.dart';
 import '../log.dart' as log;
-import '../source/hosted.dart';
 import '../utils.dart';
 
 /// Handles the `cache add` pub command.
 class CacheAddCommand extends PubCommand {
   String get name => "add";
   String get description => "Install a package.";
   String get invocation =>
       "pub cache add <package> [--version <constraint>] [--all]";
   String get docUrl => "http://dartlang.org/tools/pub/cmd/pub-cache.html";
 
@@ skipping 25 matching lines @@
     var constraint = VersionConstraint.any;
     if (argResults["version"] != null) {
       try {
         constraint = new VersionConstraint.parse(argResults["version"]);
       } on FormatException catch (error) {
         usageException(error.message);
       }
     }
 
     // TODO(rnystrom): Support installing from git too.
-    var source = cache.sources["hosted"];
+    var source = cache.source("hosted");
 
     // TODO(rnystrom): Allow specifying the server.
-    var ids = (await source.getVersions(HostedSource.refFor(package)))
+    var ids = (await source.getVersions(cache.sources.hosted.refFor(package)))
         .where((id) => constraint.allows(id.version))
         .toList();
 
     if (ids.isEmpty) {
       // TODO(rnystrom): Show most recent unmatching version?
       fail("Package $package has no versions that match $constraint.");
     }
 
     downloadVersion(id) async {
       if (cache.contains(id)) {
@@ skipping 11 matching lines @@
       // Install them in ascending order.
       ids.sort((id1, id2) => id1.version.compareTo(id2.version));
       await Future.forEach(ids, downloadVersion);
     } else {
       // Pick the best matching version.
       ids.sort((id1, id2) => Version.prioritize(id1.version, id2.version));
       await downloadVersion(ids.last);
     }
   }
 }