Add exitCode setter to set the exit code returned by the Dart VM

runtime/bin/process_patch.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.
 
 patch class _WindowsCodePageDecoder {
   /* patch */ static String _decodeBytes(List<int> bytes)
       native "SystemEncodingToString";
 }
 
 
@@ skipping 13 matching lines @@
 
   /* patch */ static Future<ProcessResult> run(String executable,
                                                List<String> arguments,
                                                [ProcessOptions options]) {
     return new _NonInteractiveProcess(executable, arguments, options)._result;
   }
 }
 
 
 patch class _ProcessUtils {
-  /* patch */ static _exit(int status) native "Exit";
+  /* patch */ static _exit(int status) native "Process_Exit";
+  /* patch */ static _setExitCode(int status) native "Process_SetExitCode";
 }
 
 
 class _ProcessStartStatus {
   int _errorCode;  // Set to OS error code if process start failed.
   String _errorMessage;  // Set to OS error message if process start failed.
 }
 
 
 class _ProcessImpl extends NativeFieldWrapperClass1 implements Process {
@@ skipping 329 matching lines @@
 
 class _ProcessResult implements ProcessResult {
   const _ProcessResult(int this.exitCode,
                        String this.stdout,
                        String this.stderr);
 
   final int exitCode;
   final String stdout;
   final String stderr;
 }