Revert "Revert "Use native async/await support in pub.""

sdk/lib/_internal/pub_generated/lib/src/source_registry.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.
-
-library pub.source_registry;
-
-import 'dart:collection';
-
-import 'package.dart';
-import 'source.dart';
-import 'source/unknown.dart';
-
-/// A class that keeps track of [Source]s used for getting packages.
-class SourceRegistry extends IterableBase<Source> {
-  final _sources = new Map<String, Source>();
-  Source _default;
-
-  /// Returns the default source, which is used when no source is specified.
-  Source get defaultSource => _default;
-
-  /// Iterates over the registered sources in name order.
-  Iterator<Source> get iterator {
-    var sources = _sources.values.toList();
-    sources.sort((a, b) => a.name.compareTo(b.name));
-    return sources.iterator;
-  }
-
-  /// Returns whether [id1] and [id2] refer to the same package, including
-  /// validating that their descriptions are equivalent.
-  bool idsEqual(PackageId id1, PackageId id2) {
-    if (id1 != id2) return false;
-    if (id1 == null && id2 == null) return true;
-    return idDescriptionsEqual(id1, id2);
-  }
-
-  /// Returns whether [id1] and [id2] have the same source and description.
-  ///
-  /// This doesn't check whether the name or versions are equal.
-  bool idDescriptionsEqual(PackageId id1, PackageId id2) {
-    if (id1.source != id2.source) return false;
-    return this[id1.source].descriptionsEqual(id1.description, id2.description);
-  }
-
-  /// Sets the default source.
-  ///
-  /// This takes a string, which must be the name of a registered source.
-  void setDefault(String name) {
-    if (!_sources.containsKey(name)) {
-      throw new StateError('Default source $name is not in the registry');
-    }
-
-    _default = _sources[name];
-  }
-
-  /// Registers a new source.
-  ///
-  /// This source may not have the same name as a source that's already been
-  /// registered.
-  void register(Source source) {
-    if (_sources.containsKey(source.name)) {
-      throw new StateError(
-          'Source registry already has a source named ' '${source.name}');
-    }
-
-    _sources[source.name] = source;
-  }
-
-  /// Returns the source named [name].
-  ///
-  /// Returns an [UnknownSource] if no source with that name has been
-  /// registered. If [name] is null, returns the default source.
-  Source operator [](String name) {
-    if (name == null) {
-      if (defaultSource != null) return defaultSource;
-      throw new StateError('No default source has been registered');
-    }
-
-    if (_sources.containsKey(name)) return _sources[name];
-    return new UnknownSource(name);
-  }
-}