Reapply change to use system code page on Windows to fix Pub.

sdk/lib/io/process.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.
 
 // TODO(ager): The only reason for this class is that we
 // cannot patch a top-level at this point.
 class _ProcessUtils {
   external static _exit(int status);
 }
 
@@ skipping 130 matching lines @@
    */
   String workingDirectory;
 
   /**
    * The encoding used for text on stdout when starting a
    * non-interactive process with [:Process.run:].
    *
    * This option is ignored for interactive processes started with
    * [:Process.start:].
    *
-   * The default stdoutEncoding is UTF_8.
+   * The default stdoutEncoding is SYSTEM.
    */
   Encoding stdoutEncoding;
 
   /**
    * The encoding used for text on stderr when starting a
    * non-interactive process with [:Process.run:].
    *
    * This option is ignored for interactive processes started with
    * [:Process.start:].
    *
-   * The default stderrEncoding is UTF_8.
+   * The default stderrEncoding is SYSTEM.
    */
   Encoding stderrEncoding;
 
   /**
    * Provides the environment variables for the process. If not set
    * the environment of the parent process is inherited.
    *
    * Currently, only ASCII environment variables are supported and
    * errors are likely to occur if an environment variables with
    * code-points outside the ASCII range is passed in.
@@ skipping 64 matching lines @@
   /**
    * Contains the system message for the process exception if any.
    */
   final String message;
 
   /**
    * Contains the OS error code for the process exception if any.
    */
   final int errorCode;
 }