Merge services into a shared IOService in dart:io, and use a native port.

runtime/bin/io_impl_sources.gypi

 # 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.
 
 # This file contains some C++ sources for the dart:io library.  The other
 # implementation files are in builtin_impl_sources.gypi.
 {
   'sources': [
     'crypto.cc',
     'crypto_android.cc',
     'crypto_linux.cc',
     'crypto_macos.cc',
     'crypto_win.cc',
     'eventhandler.cc',
     'eventhandler.h',
     'eventhandler_android.cc',
     'eventhandler_linux.cc',
     'eventhandler_linux.h',
     'eventhandler_macos.cc',
     'eventhandler_macos.h',
     'eventhandler_win.cc',
     'eventhandler_win.h',
     'filter.cc',
     'filter.h',
     'filter_unsupported.cc',
+    'io_service.cc',
+    'io_service.h',
     'net/nss_memio.cc',
     'net/nss_memio.h',
     'platform.cc',
     'platform.h',
     'platform_android.cc',
     'platform_linux.cc',
     'platform_macos.cc',
     'platform_win.cc',
     'process.cc',
     'process.h',
@@ skipping 28 matching lines @@
         'filter.cc',
         'filter.h',
         'net/nss_memio.cc',
         'net/nss_memio.h',
         'secure_socket.cc',
         'secure_socket.h',
       ],
     }],
   ],
 }