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

pkg/analyzer/test/source/package_map_provider_test.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 test.package.map.provider;
 
 import 'dart:convert';
 
 import 'package:analyzer/file_system/file_system.dart';
 import 'package:analyzer/file_system/memory_file_system.dart';
@@ skipping 34 matching lines @@
             packageName: folderPath
           }
         }).packageMap;
         expect(result, hasLength(1));
         expect(result.keys, contains(packageName));
         expect(result[packageName], hasLength(1));
         expect(result[packageName][0], new isInstanceOf<Folder>());
         expect(result[packageName][0].path, equals(folderPath));
       });
 
-      test('ignore nonexistent folder', () {
+      test("don't ignore nonexistent folder", () {
         String packageName = 'foo';
         String folderPath = '/path/to/folder';
         Map<String, List<Folder>> result = parsePackageMap({
           'packages': {
             packageName: folderPath
           }
         }).packageMap;
-        expect(result, hasLength(0));
+        expect(result, hasLength(1));
+        expect(result.keys, contains(packageName));
+        expect(result[packageName], hasLength(1));
+        expect(result[packageName][0], new isInstanceOf<Folder>());
+        expect(result[packageName][0].path, equals(folderPath));
       });
 
       test('package maps to list', () {
         String packageName = 'foo';
         String folderPath1 = '/path/to/folder1';
         String folderPath2 = '/path/to/folder2';
         resourceProvider.newFolder(folderPath1);
         resourceProvider.newFolder(folderPath2);
         Map<String, List<Folder>> result = parsePackageMap({
           'packages': {
@@ skipping 45 matching lines @@
         Set<String> dependencies = parsePackageMap({
           'packages': {},
           'input_files': [relativeDependencyPath]
         }).dependencies;
         expect(dependencies, hasLength(1));
         expect(dependencies, contains(dependencyPath));
       });
     });
   });
 }