add cache list command to pub

utils/pub/source.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 source;
 
 import 'dart:async';
 
 import '../../pkg/pathos/lib/path.dart' as path;
 
@@ skipping 197 matching lines @@
   /// the source can use the installed package to determine information about
   /// the resolved id.
   ///
   /// The returned [PackageId] may have a description field that's invalid
   /// according to [parseDescription], although it must still be serializable
   /// to JSON and YAML. It must also be equal to [id] according to
   /// [descriptionsEqual].
   ///
   /// By default, this just returns [id].
   Future<PackageId> resolveId(PackageId id) => new Future.immediate(id);
+  
+  /// Returns a list of [Package] that have been cached in in Pub's global cache

[Bob Nystrom, 2013/03/12 22:12:03]

Returns the [Package]s that have been installed in the system cache.

[keertip, 2013/03/13 15:55:00]

Done.

+  /// directory.
+  Future<List<Package>> getCachedPackages() {
+    if (shouldCache) throw "Source $name must implement this.";
+  }
 
   /// Returns the source's name.
   String toString() => name;
 }