fix MemoryResourceProvider context on Windows

pkg/analyzer/test/src/context/source_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 analyzer.test.src.context.source_test;
 
 import 'package:analyzer/file_system/file_system.dart';
 import 'package:analyzer/src/context/source.dart';
 import 'package:analyzer/src/generated/source.dart';
 import 'package:package_config/packages.dart';
@@ skipping 12 matching lines @@
 class SourceFactoryImplTest extends AbstractContextTest {
   void test_restoreUri() {
     Map<String, Uri> packageUriMap = <String, Uri>{
       'foo': Uri.parse('file:///pkgs/somepkg/lib/')
     };
     SourceFactoryImpl sourceFactory = new SourceFactoryImpl(
       <UriResolver>[new ResourceUriResolver(resourceProvider)],
       new _MockPackages(packageUriMap),
     );
     Uri uri = sourceFactory.restoreUri(newSource('/pkgs/somepkg/lib'));
-    // TODO(danrubel) fix on Windows
-    if (resourceProvider.absolutePathContext.separator != r'\') {
-      expect(uri, Uri.parse('package:foo/'));
-    }
+    expect(uri, Uri.parse('package:foo/'));
   }
 }
 
 /**
  * An implementation of [Packages] used for testing.
  */
 class _MockPackages implements Packages {
   final Map<String, Uri> map;
 
   _MockPackages(this.map);
 
   @override
   Iterable<String> get packages => map.keys;
 
   @override
   Map<String, Uri> asMap() => map;
 
   @override
   Uri resolve(Uri packageUri, {Uri notFound(Uri packageUri)}) {
     fail('Unexpected invocation of resolve');
     return null;
   }
 }