dart:io | Add test for HttpClient requests that never complete their future.

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.
 
 package/invalid_uri_test: Fail, OK # Fails intentionally
 
 [ $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
 io/socket_invalid_arguments_test: Fail, OK
 io/stdout_bad_argument_test: Fail, OK
 # These test have type errors on purpose and take very long to run in
 # checked mode with no benefit. Skip.
 io/file_fuzz_test: Skip
 io/directory_fuzz_test: Skip
 
 [ $runtime == vm && $system == macos ]
+# These tests fail intermittently on MacOS due to an https request that
+# fails not completing the future it returns: Issue 12451
+io/https_unauthorized_test: Pass, Fail
+io/https_bad_certificate_test: Pass, Fail
+
 # This test fails with "Too many open files" on the Mac OS buildbot.
 # This is expected as MacOS by default runs with a very low number
 # of allowed open files ('ulimit -n' says something like 256).
 io/socket_many_connections_test: Skip
 
 # These tests pass on MacOS 10.8.2 but fails on the buildbot machines
 # that are running an earlier version of MacOS. The issue is that the
 # old version of MacOS does not expand the precomposed utf-8 it gets
 # from the VM before comparing it to the decomposed utf-8 used for the
 # file system.
@@ skipping 118 matching lines @@
 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
 io/web_socket_ping_test: Skip # TODO(ajohnsen): Timeout issue
 
 [ $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