Transition barback's infrastructure to an aggregate-based model.

sdk/lib/_internal/pub/lib/src/barback/excluding_transformer.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 pub.excluding_transformer;
 
 import 'dart:async';
 
 import 'package:barback/barback.dart';
 
@@ skipping 19 matching lines @@
   /// assets are allowed.
   final Set<String> _includes;
 
   /// The set of assets which should be excluded.
   ///
   /// Exclusions are applied after inclusions.
   final Set<String> _excludes;
 
   ExcludingTransformer._(this._inner, this._includes, this._excludes);
 
-  Future<bool> isPrimary(AssetId id) {
+  isPrimary(AssetId id) {
     // TODO(rnystrom): Support globs in addition to paths. See #17093.
     if (_includes != null) {
       // If there are any includes, it must match one of them.
-      if (!_includes.contains(id.path)) return new Future.value(false);
+      if (!_includes.contains(id.path)) return false;
     }
 
     // It must not be excluded.
     if (_excludes != null && _excludes.contains(id.path)) {
-      return new Future.value(false);
+      return false;
     }
 
     return _inner.isPrimary(id);
   }
 
   Future apply(Transform transform) => _inner.apply(transform);
 
   String toString() => _inner.toString();
 }