More test clean-up

pkg/analyzer/test/src/task/dart_test.dart

Index: pkg/analyzer/test/src/task/dart_test.dart
diff --git a/pkg/analyzer/test/src/task/dart_test.dart b/pkg/analyzer/test/src/task/dart_test.dart
index 7489800ea2f24da4aa80766bd84586bea490f854..b9745636cafd1915bcc579ee42aeff565cec5c57 100644
--- a/pkg/analyzer/test/src/task/dart_test.dart
+++ b/pkg/analyzer/test/src/task/dart_test.dart
@@ -927,10 +927,13 @@ part 'part.dart';
   }
 
   test_perform_invalidUri_part() {
+    String invalidUri = resourceProvider.pathContext.separator == '/'
+        ? '//////////'
+        : '\\\\\\\\\\\\';
     _performBuildTask({
       '/lib.dart': '''
 library lib;
-part '//////////';
+part '$invalidUri';
 '''
     });
     expect(libraryElement.parts, isEmpty);