Use patching for dart:io.

runtime/bin/platform.dart

-// 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.
-
-/**
- * The [Platform] class exposes details of the machine and operating
- * system.
- */
-class Platform {
-  /**
-   * Get the number of processors of the machine.
-   */
-  static int get numberOfProcessors => _Platform.numberOfProcessors;
-
-  /**
-   * Get the path separator used by the operating system to separate
-   * components in file paths.
-   */
-  static String get pathSeparator => _Platform.pathSeparator;
-
-  /**
-   * Get a string ('macos', 'windows', 'linux') representing the
-   * operating system.
-   */
-  static String get operatingSystem => _Platform.operatingSystem;
-
-  /**
-   * Get the local hostname for the system.
-   */
-  static String get localHostname => _Platform.localHostname;
-
-  /**
-   * Get the environment for this process.
-   */
-  static Map<String, String> get environment => _Platform.environment;
-}