Don't do folder existence checks when parsing pub list results.

pkg/analyzer/lib/source/pub_package_map_provider.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 source.pub_package_map_provider;
 
 import 'dart:collection';
 import 'dart:convert';
 import 'dart:io' as io;
 
@@ skipping 77 matching lines @@
     //     "path/to/myapp/pubspec.lock"
     //   ]
     // }
     Map<String, List<Folder>> packageMap = new HashMap<String, List<Folder>>();
     Map obj = JSON.decode(jsonText);
     Map packages = obj['packages'];
     processPaths(String packageName, List paths) {
       List<Folder> folders = <Folder>[];
       for (var path in paths) {
         if (path is String) {
-          Resource resource = folder.getChild(path);
+          Resource resource = folder.getChildAssumingFolder(path);
           if (resource is Folder) {
             folders.add(resource);
           }
         }
       }
       if (folders.isNotEmpty) {
         packageMap[packageName] = folders;
       }
     }
     packages.forEach((key, value) {
@@ skipping 20 matching lines @@
    */
   PackageMapInfo _error(Folder folder) {
     // Even if an error occurs, we still need to know the dependencies, so that
     // we'll know when to try running "pub list-package-dirs" again.
     // Unfortunately, "pub list-package-dirs" doesn't tell us dependencies when
     // an error occurs, so just assume there is one dependency, "pubspec.lock".
     List<String> dependencies = <String>[join(folder.path, PUBSPEC_LOCK_NAME)];
     return new PackageMapInfo(null, dependencies.toSet());
   }
 }