Support directories other than "web" in pub build.

sdk/lib/_internal/pub/lib/src/barback/dart_forwarding_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.dart_forwarding_transformer;
 
 import 'dart:async';
 
 import 'package:barback/barback.dart';
 
 import '../utils.dart';
 
 /// A single transformer that just forwards any ".dart" file as an output when
 /// not in release mode.
 ///
 /// Since the [Dart2JSTransformer] consumes its inputs, this is used in
 /// parallel to make sure the original Dart file is still available for use by
-/// Dartium. In release mode, it's used to the do the exact opposite: it
-/// ensures that no Dart files are emitted, since all that is deployed is the
-/// compiled JavaScript.
+/// Dartium.
 class DartForwardingTransformer extends Transformer {
   /// The mode that the transformer is running in.
   final BarbackMode _mode;
 
   DartForwardingTransformer(this._mode);
 
   String get allowedExtensions => ".dart";
 
   Future apply(Transform transform) {
     return newFuture(() {
-      if (_mode != BarbackMode.RELEASE) {
-        transform.addOutput(transform.primaryInput);
-      }
+      transform.addOutput(transform.primaryInput);
     });
   }
 }