First stab at a dev server in pub using barback.

sdk/lib/_internal/pub/lib/src/command.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.
 
 library pub.command;
 
 import 'dart:io';
 import 'dart:async';
 
 import 'package:args/args.dart';
 import 'package:path/path.dart' as path;
 
 import 'command/cache.dart';
 import 'command/deploy.dart';
 import 'command/help.dart';
 import 'command/install.dart';
 import 'command/lish.dart';
+import 'command/serve.dart';
 import 'command/update.dart';
 import 'command/uploader.dart';
 import 'command/version.dart';
 import 'entrypoint.dart';
 import 'exit_codes.dart' as exit_codes;
 import 'http.dart';
 import 'log.dart' as log;
 import 'package.dart';
 import 'system_cache.dart';
 import 'utils.dart';
@@ skipping 158 matching lines @@
   }
 }
 
 _initCommands() {
   var commands = {
     'cache': new CacheCommand(),
     'deploy': new DeployCommand(),
     'help': new HelpCommand(),
     'install': new InstallCommand(),
     'publish': new LishCommand(),
+    'serve': new ServeCommand(),
     'update': new UpdateCommand(),
     'uploader': new UploaderCommand(),
     'version': new VersionCommand()
   };
 
   for (var command in commands.values.toList()) {
     for (var alias in command.aliases) {
       commands[alias] = command;
     }
   }
 
   return commands;
 }