Fix flaky http test and reenable on buildbots.

tests/standalone/standalone.status

 # Copyright (c) 2012, 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.
 
 out_of_memory_test: Skip # Issue 2345
 
 package/invalid_uri_test: Fail, OK # Fails intentionally
 
 [ $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
 # 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 ]
 io/many_echo_server_test: Skip        # Bug 5103754
-# This test fails intermittently.
-io/http_basic_test: Pass, Fail     # Issue 3599
 
 [ $runtime == vm && $system == linux ]
 io/test_runner_test: Pass, Fail  # Issue 1947
 
 [ $runtime == vm && $system == macos ]
 # This test fails with "Too many open files" on the Mac OS buildbot.
 io/socket_many_connections_test: Skip
 io/http_server_handler_test: Skip # Issue 2637
 
 [ $runtime == vm && $system == windows ]
@@ skipping 36 matching lines @@
 [ $compiler == dart2js && $browser ]
 *: Skip
 
 [ $compiler == dart2js && $checked ]
 io/http_read_test: Skip # Timeout TODO(ngeoffray): investigate
 io/list_input_stream_test: Skip # Timeout TODO(ngeoffray): investigate
 
 [ $compiler == dart2dart ]
 # Skip until we stabilize language tests.
 *: Skip