Start implementing pub object model. Rudimentary package cache class, and a simple pub command to l…

utils/pub/command_list.dart

Index: utils/pub/command_list.dart
diff --git a/utils/pub/command_list.dart b/utils/pub/command_list.dart
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+// 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.
+
+/** Handles the `list` pub command. */
+void commandList(PubOptions options, List<String> args) {
+  // TODO(rnystrom): Validate args. Right now, this just lists the packages in
+  // your cache.
+  final cache = new PackageCache(options.cacheDir);
+  cache.listAll().then((packages) {
+    for (final package in packages) {
+      print(package.name);
+    }
+  });
+}