Use patching for dart:io.

lib/io/iolib_sources.gypi

Index: lib/io/iolib_sources.gypi
diff --git a/runtime/bin/io_sources.gypi b/lib/io/iolib_sources.gypi
similarity index 72%
copy from runtime/bin/io_sources.gypi
copy to lib/io/iolib_sources.gypi
index 35d13aa75d8f78c8a458ba5af28f1c313df33cb5..55a9bcf81d714c7bea8d03f4176d6355b9b389b5 100644
--- a/runtime/bin/io_sources.gypi
+++ b/lib/io/iolib_sources.gypi
@@ -2,15 +2,8 @@
 # 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 all sources for the dart:io library.
 {
   'sources': [
-    # The io.dart file needs to be the first source file. It contains
-    # the library and import directives for the dart:io library. The
-    # dart:io library is created by concatenating the files listed here
-    # in the order they are listed.
-    'io.dart',
-
     'base64.dart',
     'buffer_list.dart',
     'chunked_stream.dart',
@@ -35,9 +28,7 @@
     'platform.dart',
     'platform_impl.dart',
     'process.dart',
-    'process_impl.dart',
     'socket.dart',
-    'socket_impl.dart',
     'socket_stream_impl.dart',
     'stdio.dart',
     'stream_util.dart',