Don't require Transformer methods to return Futures.

sdk/lib/_internal/pub/lib/src/barback/dart2js_transformer.dart

 // 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 pub.dart2js_transformer;
 
 import 'dart:async';
 import 'dart:convert';
 
 import 'package:analyzer/analyzer.dart';
@@ skipping 41 matching lines @@
 
     throw new FormatException("Unrecognized dart2js "
         "${pluralize('option', invalidOptions.length)} "
         "${toSentence(invalidOptions.map((option) => '"$option"'))}.");
   }
 
   Dart2JSTransformer(AssetEnvironment environment, BarbackMode mode)
       : this.withSettings(environment, new BarbackSettings({}, mode));
 
   /// Only ".dart" entrypoint files within a buildable directory are processed.
-  Future<bool> isPrimary(AssetId id) {
-    if (id.extension != ".dart") return new Future.value(false);
+  bool isPrimary(AssetId id) {
+    if (id.extension != ".dart") return false;
 
     // These should only contain libraries. For efficiency's sake, we don't
     // look for entrypoints in there.
-    return new Future.value(!["asset/", "lib/"].any(id.path.startsWith));
+    return !["asset/", "lib/"].any(id.path.startsWith);
   }
 
   Future apply(Transform transform) {
     // TODO(nweiz): If/when barback starts reporting what assets were modified,
     // don't re-run the entrypoint detection logic unless the primary input was
     // actually modified. See issue 16817.
     return _isEntrypoint(transform.primaryInput).then((isEntrypoint) {
       if (!isEntrypoint) return null;
 
       // Wait for any ongoing apply to finish first.
       return _pool.withResource(() {
         transform.logger.info("Compiling ${transform.primaryInput.id}...");
         var stopwatch = new Stopwatch()..start();
         return _doCompilation(transform).then((_) {
           stopwatch.stop();
           transform.logger.info("Took ${stopwatch.elapsed} to compile "
               "${transform.primaryInput.id}.");
         });
       });
     });
   }
 
-  Future declareOutputs(DeclaringTransform transform) {
+  void declareOutputs(DeclaringTransform transform) {
     var primaryId = transform.primaryId;
     transform.declareOutput(primaryId.addExtension(".js"));
     transform.declareOutput(primaryId.addExtension(".precompiled.js"));
     if (_generateSourceMaps) {
       transform.declareOutput(primaryId.addExtension(".js.map"));
     }
-    return new Future.value();
   }
 
   /// Returns whether or not [asset] might be an entrypoint.
   Future<bool> _isEntrypoint(Asset asset) {
     return asset.readAsString().then((code) {
       try {
         var name = asset.id.path;
         if (asset.id.package != _environment.rootPackage.name) {
           name += " in ${asset.id.package}";
         }
@@ skipping 292 matching lines @@
   }
 }
 
 /// An [EventSink] that discards all data. Provided to dart2js when we don't
 /// want an actual output.
 class NullSink<T> implements EventSink<T> {
   void add(T event) {}
   void addError(errorEvent, [StackTrace stackTrace]) {}
   void close() {}
 }