Fix a bug in barback's static package handling.

pkg/barback/lib/src/graph/static_asset_cascade.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 barback.graph.static_asset_cascade;
 
 import 'dart:async';
 
 import '../asset/asset_id.dart';
 import '../asset/asset_node.dart';
@@ skipping 24 matching lines @@
   final _errorsController =
       new StreamController<BarbackException>.broadcast(sync: true);
 
   final status = NodeStatus.IDLE;
 
   final onLog = new StreamController<LogEntry>.broadcast().stream;
   final onStatusChange = new StreamController<LogEntry>.broadcast().stream;
 
   Future<AssetSet> get availableOutputs {
     var provider = graph.provider as StaticPackageProvider;
-    return provider.getAllAssetIds(package).map(provider.getAsset).toList()
+    return provider.getAllAssetIds(package).asyncMap(provider.getAsset).toList()
         .then((assets) => new AssetSet.from(assets));
   }
 
   Future<AssetNode> getAssetNode(AssetId id) {
     return _sources.putIfAbsent(id, () {
       return graph.provider.getAsset(id).then((asset) {
         return new AssetNodeController.available(asset).node;
       }).catchError((error, stackTrace) {
         if (error is! AssetNotFoundException) {
           reportError(new AssetLoadException(id, error, stackTrace));
@@ skipping 16 matching lines @@
   void updateTransformers(Iterable<Iterable> transformersIterable) =>
       throw new UnsupportedError("Static package $package can't have "
           "transformers.");
 
   void forceAllTransforms() {}
 
   void reportError(BarbackException error) => _errorsController.add(error);
 
   String toString() => "static cascade for $package";
 }