Allow multiple dirs per package in the data returned by "pub list".

pkg/analysis_server/test/mocks.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 mocks;
 
 import 'dart:async';
 import 'dart:io';
 
 @MirrorsUsed(targets: 'mocks', override: '*')
@@ skipping 397 matching lines @@
 
   // Not used.
   @override
   List<String> get uris => throw unimplemented;
 }
 
 /**
  * A mock [PackageMapProvider].
  */
 class MockPackageMapProvider implements PackageMapProvider {
-  Map<String, resource.Folder> packageMap = <String, resource.Folder>{};
+  Map<String, List<resource.Folder>> packageMap = <String, List<resource.Folder>>{};
 
   @override
-  Map<String, resource.Folder> computePackageMap(resource.Folder folder) {
+  Map<String, List<resource.Folder>> computePackageMap(resource.Folder folder) {
     return packageMap;
   }
 }