Fix complex_reload_test on Windows

runtime/observatory/tests/service/complex_reload_test.dart

 // Copyright (c) 2016, 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.
 // VMOptions=--error_on_bad_type --error_on_bad_override
 
 import 'test_helper.dart';
 import 'dart:async';
 import 'dart:developer';
 import 'dart:isolate' as I;
 import 'dart:io';
 import 'service_test_common.dart';
 import 'package:observatory/service.dart';
 import 'package:path/path.dart' as path;
 import 'package:unittest/unittest.dart';
 
 // Chop off the file name.
 String baseDirectory =
-    path.dirname(Platform.script.path) + Platform.pathSeparator;
+    path.dirname(Platform.script.path) + '/';
 
 Uri baseUri = Platform.script.replace(path: baseDirectory);
 Uri spawnUri = baseUri.resolveUri(Uri.parse('complex_reload/v1/main.dart'));
 Uri v2Uri = baseUri.resolveUri(Uri.parse('complex_reload/v2/main.dart'));
 Uri v3Uri = baseUri.resolveUri(Uri.parse('complex_reload/v3/main.dart'));
 
 testMain() async {
   print(baseUri);
   debugger();  // Stop here.
   // Spawn the child isolate.
@@ skipping 52 matching lines @@
     );
     expect(response['success'], isTrue);
 
     // Invoke test in v3.
     String v3 = await invokeTest(slaveIsolate);
     expect(v3, 'cabbage');
   }
 ];
 
 main(args) => runIsolateTests(args, tests, testeeConcurrent: testMain);