Add a Resource.parent getter, which gets the parent directory.

pkg/analysis_server/test/resource_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.resource;
 
 import 'dart:async';
 
 import 'package:analysis_server/src/resource.dart';
 import 'package:analyzer/src/generated/engine.dart' show TimestampedData;
@@ skipping 241 matching lines @@
 
       test('shortName', () {
         File file = provider.getResource('/foo/bar/file.txt');
         expect(file.shortName, 'file.txt');
       });
 
       test('toString', () {
         File file = provider.getResource('/foo/bar/file.txt');
         expect(file.toString(), '/foo/bar/file.txt');
       });
+
+      test('parent', () {
+        provider.newFile('/foo/bar/file.txt', 'content');
+        File file = provider.getResource('/foo/bar/file.txt');
+        Resource parent = file.parent;
+        expect(parent, new isInstanceOf<Folder>());
+        expect(parent.path, equals('/foo/bar'));
+      });
     });
 
     group('Folder', () {
       Folder folder;
 
       setUp(() {
         folder = provider.newFolder('/foo/bar');
       });
 
       group('getChild', () {
@@ skipping 32 matching lines @@
         });
         // check names
         expect(children[0].shortName, 'a.txt');
         expect(children[1].shortName, 'bFolder');
         expect(children[2].shortName, 'c.txt');
         // check types
         expect(children[0], _isFile);
         expect(children[1], _isFolder);
         expect(children[2], _isFile);
       });
+
+      test('parent', () {
+        Resource parent1 = folder.parent;
+        expect(parent1, new isInstanceOf<Folder>());
+        expect(parent1.path, equals('/foo'));
+        Resource parent2 = parent1.parent;
+        expect(parent2, new isInstanceOf<Folder>());
+        expect(parent2.path, equals('/'));
+        expect(parent2.parent, isNull);
+      });
     });
 
     group('_MemoryFileSource', () {
       Source source;
 
       group('existent', () {
         setUp(() {
           File file = provider.newFile('/foo/test.dart', 'library test;');
           source = file.createSource(UriKind.FILE_URI);
         });
@@ skipping 144 matching lines @@
       expect(source, isNull);
     });
 
     test('not a file URI', () {
       var uri = new Uri(scheme: 'https', path: '127.0.0.1/test.dart');
       Source source = resolver.resolveAbsolute(uri);
       expect(source, isNull);
     });
   });
 }