Fix off-by-one bug in many_files_test.

sdk/lib/_internal/pub/test/lish/many_files_test.dart

 // Copyright (c) 2015, 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 'dart:convert';
 import 'dart:io';
 import 'dart:math' as math;
 
 import 'package:path/path.dart' as p;
 import 'package:scheduled_test/scheduled_test.dart';
 import 'package:scheduled_test/scheduled_server.dart';
 import 'package:shelf/shelf.dart' as shelf;
 
 import '../../lib/src/exit_codes.dart' as exit_codes;
 import '../descriptor.dart' as d;
 import '../test_pub.dart';
 import 'utils.dart';
 
 /// The maximum number of bytes in an entire path.
 ///
 /// This is [Windows's number][MAX_PATH], which is a much tighter constraint
-/// than OS X or Linux. We use it everywhere for consistency.
+/// than OS X or Linux. We subtract one because Windows counts it as the number
+/// of bytes in a path C string including the terminating NUL but we only count
+/// characters here.
+///
+/// We use this limit on all platforms for consistency.
 ///
 /// [MAX_PATH]: https://msdn.microsoft.com/en-us/library/windows/desktop/aa383130(v=vs.85).aspx
-const _pathMax = 260;
+const _pathMax = 260 - 1;
 
 main() {
   initConfig();
 
   integration('archives and uploads a package with more files than can fit on '
       'the command line', () {
     d.validPackage.create();
 
     var argMax;
     if (Platform.isWindows) {
@@ skipping 49 matching lines @@
       return new shelf.Response.ok(JSON.encode({
         'success': {'message': 'Package test_pkg 1.0.0 uploaded!'}
       }));
     });
 
     pub.stdout.expect(startsWith('Uploading...'));
     pub.stdout.expect('Package test_pkg 1.0.0 uploaded!');
     pub.shouldExit(exit_codes.SUCCESS);
   });
 }