Mark process_sync_test as slow on windows.

tests/standalone/standalone.status

 # Copyright (c) 2013, 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.
 
 # WARNING:
 # Tests using the multitest feature where failure is expected should *also* be
 # listed in tests/lib/analyzer/analyze_tests.status without the "standalone"
 # prefix.
 
 # The testing infrastructure is using the dart:io Path and LineTransformer
 # classes.
 io/skipping_dart2js_compilations_test: Skip # http/dartbug.com/12449
 io/dependency_graph_test: Skip # http/dartbug.com/12449
 io/status_file_parser_test: Skip # http/dartbug.com/12449
 
 package/invalid_uri_test: Fail, OK # Fails intentionally
 
 [ $runtime == vm && $system == windows ]
 io/file_system_watcher_test: Pass, Timeout # Issue 13228
+io/process_sync_test: Pass, Timeout # Issue 13541
 
 [ $runtime == vm ]
 package/package_isolate_test: Fail # http://dartbug.com/7520.
 
 
 [ $runtime == vm && $checked ]
 # These tests have type errors on purpose.
 io/process_invalid_arguments_test: Fail, OK
 io/directory_invalid_arguments_test: Fail, OK
 io/file_invalid_arguments_test: Fail, OK
@@ skipping 142 matching lines @@
 io/web_socket_test: Pass, Slow
 io/http_server_response_test: Pass, Slow
 out_of_memory_test: Skip # passes on Mac, crashes on Linux
 oom_error_stacktrace_test: Skip # Fails on Linux
 
 [ $arch == mips ]
 io/test_extension_test: Fail
 io/test_extension_fail_test: Fail
 io/dart_std_io_pipe_test: Fail
 io/file_read_special_device_test: Fail