Roll Observatory packages and add a roll script

args/lib/src/help_command.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.
-
-library args.help_command;
-
-import '../command_runner.dart';
-
-/// The built-in help command that's added to every [CommandRunner].
-///
-/// This command displays help information for the various subcommands.
-class HelpCommand extends Command {
-  final name = "help";
-  String get description =>
-      "Display help information for ${runner.executableName}.";
-  String get invocation => "${runner.executableName} help [command]";
-
-  void run() {
-    // Show the default help if no command was specified.
-    if (argResults.rest.isEmpty) {
-      runner.printUsage();
-      return;
-    }
-
-    // Walk the command tree to show help for the selected command or
-    // subcommand.
-    var commands = runner.commands;
-    var command = null;
-    var commandString = runner.executableName;
-
-    for (var name in argResults.rest) {
-      if (commands.isEmpty) {
-        command.usageException(
-            'Command "$commandString" does not expect a subcommand.');
-      }
-
-      if (commands[name] == null) {
-        if (command == null) {
-          runner.usageException('Could not find a command named "$name".');
-        }
-
-        command.usageException(
-            'Could not find a subcommand named "$name" for "$commandString".');
-      }
-
-      command = commands[name];
-      commands = command.subcommands;
-      commandString += " $name";
-    }
-
-    command.printUsage();
-  }
-}