Add observatory_pub_packages snapshot to third_party

observatory_pub_packages/barback/src/asset/asset_set.dart

Index: observatory_pub_packages/barback/src/asset/asset_set.dart
===================================================================
--- observatory_pub_packages/barback/src/asset/asset_set.dart	(revision 0)
+++ observatory_pub_packages/barback/src/asset/asset_set.dart	(working copy)
@@ -0,0 +1,76 @@
+// 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 barback.asset.asset_set;
+
+import 'dart:collection';
+
+import 'asset.dart';
+import 'asset_id.dart';
+
+/// A set of [Asset]s with distinct IDs.
+///
+/// This uses the [AssetId] of each asset to determine uniqueness, so no two
+/// assets with the same ID can be in the set.
+class AssetSet extends IterableBase<Asset> {
+  final _assets = new Map<AssetId, Asset>();
+
+  /// The ids of the assets in the set.
+  Iterable<AssetId> get ids => _assets.keys;
+
+  AssetSet();
+
+  /// Creates a new AssetSet from the contents of [other].
+  ///
+  /// If multiple assets in [other] have the same id, the last one takes
+  /// precedence.
+  AssetSet.from(Iterable<Asset> other) {
+    for (var asset in other) {
+      _assets[asset.id] = asset;
+    }
+  }
+
+  Iterator<Asset> get iterator => _assets.values.iterator;
+
+  int get length => _assets.length;
+
+  /// Gets the [Asset] in the set with [id], or returns `null` if no asset with
+  /// that ID is present.
+  Asset operator[](AssetId id) => _assets[id];
+
+  /// Adds [asset] to the set.
+  ///
+  /// If there is already an asset with that ID in the set, it is replaced by
+  /// the new one. Returns [asset].
+  Asset add(Asset asset) {
+    _assets[asset.id] = asset;
+    return asset;
+  }
+
+  /// Adds [assets] to the set.
+  void addAll(Iterable<Asset> assets) {
+    assets.forEach(add);
+  }
+
+  /// Returns `true` if the set contains [asset].
+  bool contains(Asset asset) {
+    var other = _assets[asset.id];
+    return other == asset;
+  }
+
+  /// Returns `true` if the set contains an [Asset] with [id].
+  bool containsId(AssetId id) {
+    return _assets.containsKey(id);
+  }
+
+  /// If the set contains an [Asset] with [id], removes and returns it.
+  Asset removeId(AssetId id) => _assets.remove(id);
+
+  /// Removes all assets from the set.
+  void clear() {
+    _assets.clear();
+  }
+
+  String toString() => _assets.toString();
+}