Get binstubs working on Windows.

sdk/lib/_internal/pub/test/global/binstubs/binstub_runs_precompiled_snapshot_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.
 
 import 'package:scheduled_test/scheduled_test.dart';
 
 import '../../descriptor.dart' as d;
 import '../../test_pub.dart';
+import 'utils.dart';
 
 main() {
   initConfig();
   integration("the binstubs runs a precompiled snapshot if present", () {
     servePackages((builder) {
       builder.serve("foo", "1.0.0", pubspec: {
         "executables": {
           "foo-script": "script"
         }
       }, contents: [
         d.dir("bin", [
           d.file("script.dart", "main(args) => print('ok');")
         ])
       ]);
     });
 
     schedulePub(args: ["global", "activate", "foo"]);
 
     d.dir(cachePath, [
       d.dir("bin", [
-        d.matcherFile("foo-script", contains("script.dart.snapshot"))
+        d.matcherFile(binStubName("foo-script"),
+            contains("script.dart.snapshot"))
       ])
     ]).validate();
   });
 }