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

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.
 
 part of dart.io;
 
 // 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);
+  external static _setExitCode(int status);
 }
 
-/** Exit the Dart VM process with the given [status] code. */
+/**
+ * Exit the Dart VM process immediately with the given [status] code.
+ *
+ * This does not wait for any asynchronous operations to terminate. Using
+ * [exit] is therefore very likely to lose data.
+ */
 void exit(int status) {
   if (status is !int) {
-    throw new ArgumentError("int status expected");
+    throw new ArgumentError("exit: int status expected");
   }
   _ProcessUtils._exit(status);
 }
 
 /**
+ * Global exit code for the Dart VM.
+ *
+ * The exit code is global for the Dart VM and the last assignment to
+ * exitCode from any isolate determines the exit code of the Dart VM
+ * on normal termination.
+ */
+set exitCode(int status) {
+  if (status is !int) {
+    throw new ArgumentError("setExitCode: int status expected");
+  }
+  _ProcessUtils._setExitCode(status);
+}
+
+/**
  * [Process] is used to start new processes using the static
  * [start] and [run] methods.
  */
 abstract class Process {
   /**
    * Starts a process running the [executable] with the specified
    * [arguments]. Returns a [:Future<Process>:] that completes with a
    * Process instance when the process has been successfully
    * started. That [Process] object can be used to interact with the
    * process. If the process cannot be started the returned [Future]
@@ skipping 207 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;
 }