Fix context/builder_test.dart on Windows.

pkg/analyzer/test/src/context/builder_test.dart

Index: pkg/analyzer/test/src/context/builder_test.dart
diff --git a/pkg/analyzer/test/src/context/builder_test.dart b/pkg/analyzer/test/src/context/builder_test.dart
index 73f3b450e563c980c5bc6393b6a8fb27dc21e889..895a7f1619f5a6b804798e6731d48e71891a3634 100644
--- a/pkg/analyzer/test/src/context/builder_test.dart
+++ b/pkg/analyzer/test/src/context/builder_test.dart
@@ -96,7 +96,8 @@ const Map<String, LibraryInfo> libraries = const {
     resourceProvider = new MemoryResourceProvider();
     pathContext = resourceProvider.pathContext;
     new MockSdk(resourceProvider: resourceProvider);
-    sdkManager = new DartSdkManager('/sdk', false, (_) {
+    sdkManager =
+        new DartSdkManager(resourceProvider.convertPath('/sdk'), false, (_) {
       fail('Should not be used to create an SDK');
     });
     contentCache = new ContentCache();