Refactor command code and add support for --help and --version.

utils/pub/command_list.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.
 
-/** 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.
-  cache.listAll().then((packages) {
-    packages.sort((a, b) => a.name.compareTo(b.name));
-    for (final package in packages) {
-      print(package.name);
-    }
-  });
-}
+/**
+ * Handles the `list` pub command. This is mostly just used so we can pull
+ * some basic data out of pub in the integration tests. Once pub is more
+ * full-featured and has other commands that test everything it does, this
+ * may go away.
+ */
+class ListCommand extends PubCommand {
+  String get description() => 'print the contents of repositories';
+
+  void onRun() {
+    cache.listAll().then((packages) {
+      for (final package in packages) {
+        print(package.name);
+      }
+    });
+  }
+}