Roll Observatory packages and add a roll script

package_config/lib/packages.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.
-
-library package_config.packages;
-
-import "src/packages_impl.dart";
-
-/// A package resolution strategy.
-///
-/// Allows converting a `package:` URI to a different kind of URI.
-///
-/// May also allow listing the available packages and converting
-/// to a `Map<String, Uri>` that gives the base location of each available
-/// package. In some cases there is no way to find the available packages,
-/// in which case [packages] and [asMap] will throw if used.
-/// One such case is if the packages are resolved relative to a
-/// `packages/` directory available over HTTP.
-abstract class Packages {
-
-  /// A [Packages] resolver containing no packages.
-  ///
-  /// This constant object is returned by [find] above if no
-  /// package resolution strategy is found.
-  static const Packages noPackages = const NoPackages();
-
-  /// Resolve a package URI into a non-package URI.
-  ///
-  /// Translates a `package:` URI, according to the package resolution
-  /// strategy, into a URI that can be loaded.
-  /// By default, only `file`, `http` and `https` URIs are returned.
-  /// Custom `Packages` objects may return other URIs.
-  ///
-  /// If resolution fails because a package with the requested package name
-  /// is not available, the [notFound] function is called.
-  /// If no `notFound` function is provided, it defaults to throwing an error.
-  ///
-  /// The [packageUri] must be a valid package URI.
-  Uri resolve(Uri packageUri, {Uri notFound(Uri packageUri)});
-
-  /// Return the names of the available packages.
-  ///
-  /// Returns an iterable that allows iterating the names of available packages.
-  ///
-  /// Some `Packages` objects are unable to find the package names,
-  /// and getting `packages` from such a `Packages` object will throw.
-  Iterable<String> get packages;
-
-  /// Return the names-to-base-URI mapping of the available packages.
-  ///
-  /// Returns a map from package name to a base URI.
-  /// The [resolve] method will resolve a package URI with a specific package
-  /// name to a path extending the base URI that this map gives for that
-  /// package name.
-  ///
-  /// Some `Packages` objects are unable to find the package names,
-  /// and calling `asMap` on such a `Packages` object will throw.
-  Map<String, Uri> asMap();
-}