Support serving from multiple directories using "pub serve".

sdk/lib/_internal/pub/lib/src/barback/load_transformers.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.load_transformers;
 
 import 'dart:async';
 import 'dart:convert';
 import 'dart:isolate';
 
@@ skipping 348 matching lines @@
   return controller.stream;
 }
 """;
 
 /// Load and return all transformers and groups from the library identified by
 /// [id].
 Future<Set> loadTransformers(BuildEnvironment environment, TransformerId id) {
   return id.getAssetId(environment.barback).then((assetId) {
     var path = assetId.path.replaceFirst('lib/', '');
     // TODO(nweiz): load from a "package:" URI when issue 12474 is fixed.
-    var baseUrl = baseUrlForAddress(environment.server.address,
-                                    environment.server.port);
+    var baseUrl = baseUrlForAddress(environment.servers.first.address,
+                                    environment.servers.first.port);

[Bob Nystrom, 2014/02/19 00:36:52]

Document why using .first is OK.

[nweiz, 2014/02/19 01:25:58]

Done.

     var uri = '$baseUrl/packages/${id.package}/$path';
     var code = 'import "$uri";\n' +
         _TRANSFORMER_ISOLATE.replaceAll('<<URL_BASE>>', baseUrl);
     log.fine("Loading transformers from $assetId");
 
     var port = new ReceivePort();
     return dart.runInIsolate(code, port.sendPort)
         .then((_) => port.first)
         .then((sendPort) {
       return _call(sendPort, {
@@ skipping 172 matching lines @@
   });
 
   return Chain.track(receivePort.first).then((response) {
     if (response['type'] == 'success') return response['value'];
     assert(response['type'] == 'error');
     return new Future.error(
         new dart.CrossIsolateException.deserialize(response['error']),
         new Chain.current());
   });
 }