Roll Observatory packages and add a roll script

package_config/lib/src/packages_io_impl.dart

-// Copyright (c) 2015, 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.
-
-/// Implementations of [Packages] that can only be used in server based
-/// applications.
-library package_config.packages_io_impl;
-
-import "dart:collection" show UnmodifiableMapView;
-import "dart:io" show Directory;
-import "package:path/path.dart" as path;
-import "packages_impl.dart";
-
-/// A [Packages] implementation based on a local directory.
-class FilePackagesDirectoryPackages extends PackagesBase {
-  final Directory _packageDir;
-  FilePackagesDirectoryPackages(this._packageDir);
-
-  Uri getBase(String packageName) =>
-    new Uri.file(path.join(_packageDir.path, packageName, '.'));
-
-  Iterable<String> _listPackageNames() {
-    return _packageDir.listSync()
-    .where((e) => e is Directory)
-    .map((e) => path.basename(e.path));
-  }
-
-  Iterable<String> get packages => _listPackageNames();
-
-  Map<String, Uri> asMap() {
-    var result = <String, Uri>{};
-    for (var packageName in _listPackageNames()) {
-      result[packageName] = getBase(packageName);
-    }
-    return new UnmodifiableMapView<String, Uri>(result);
-  }
-}