Use patching for dart:io.

runtime/bin/platform_patch.dart

Index: runtime/bin/platform_patch.dart
diff --git a/runtime/bin/platform_patch.dart b/runtime/bin/platform_patch.dart
new file mode 100644
index 0000000000000000000000000000000000000000..02ba12967f94d89c959b721e11e7b4a9b1028f34
--- /dev/null
+++ b/runtime/bin/platform_patch.dart
@@ -0,0 +1,13 @@
+// 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.
+
+patch class _Platform {
+  /* patch */ static int _numberOfProcessors()
+      native "Platform_NumberOfProcessors";
+  /* patch */ static String _pathSeparator() native "Platform_PathSeparator";
+  /* patch */ static String _operatingSystem()
+      native "Platform_OperatingSystem";
+  /* patch */ static _localHostname() native "Platform_LocalHostname";
+  /* patch */ static _environment() native "Platform_Environment";
+}