Fix more tests on windows bots

pkg/analyzer/test/src/dart/sdk/sdk_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.generated.sdk_test;
 
 import 'package:analyzer/file_system/file_system.dart';
 import 'package:analyzer/file_system/memory_file_system.dart';
 import 'package:analyzer/src/context/builder.dart' show EmbedderYamlLocator;
 import 'package:analyzer/src/dart/sdk/sdk.dart';
@@ skipping 323 matching lines @@
 };
 ''';
 }
 
 @reflectiveTest
 class SdkExtensionFinderTest {
   MemoryResourceProvider resourceProvider;
 
   void setUp() {
     resourceProvider = new MemoryResourceProvider();
-    resourceProvider.newFolder('/empty');
-    resourceProvider.newFolder('/tmp');
+    resourceProvider.newFolder(resourceProvider.convertPath('/empty'));
+    resourceProvider.newFolder(resourceProvider.convertPath('/tmp'));
     resourceProvider.newFile(
-        '/tmp/_sdkext',
+        resourceProvider.convertPath('/tmp/_sdkext'),
         r'''
 {
   "dart:fox": "slippy.dart",
   "dart:bear": "grizzly.dart",
   "dart:relative": "../relative.dart",
   "dart:deep": "deep/directory/file.dart",
   "fart:loudly": "nomatter.dart"
 }''');
   }
 
@@ skipping 107 matching lines @@
     expect(second, isNotNull);
     expect(second.category, "Server");
     expect(second.path, "second/second.dart");
     expect(second.shortName, "dart:second");
     expect(second.isDart2JsLibrary, false);
     expect(second.isDocumented, false);
     expect(second.isImplementation, true);
     expect(second.isVmLibrary, false);
   }
 }