Add support for starting a detached process

sdk/lib/io/process.dart

 // Copyright (c) 2014, 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 void _exit(int status);
@@ skipping 223 matching lines @@
    * Use [environment] to set the environment variables for the process. If not
    * set the environment of the parent process is inherited. Currently, only
    * US-ASCII environment variables are supported and errors are likely to occur
    * if an environment variable with code-points outside the US-ASCII range is
    * passed in.
    *
    * If [includeParentEnvironment] is `true`, the process's environment will
    * include the parent process's environment, with [environment] taking
    * precedence. Default is `true`.
    *
-   * If [runInShell] is true, the process will be spawned through a system
+   * If [runInShell] is `true`, the process will be spawned through a system
    * shell. On Linux and Mac OS, [:/bin/sh:] is used, while
    * [:%WINDIR%\system32\cmd.exe:] is used on Windows.
    *
    * Users must read all data coming on the [stdout] and [stderr]
    * streams of processes started with [:Process.start:]. If the user
    * does not read all data on the streams the underlying system
    * resources will not be freed since there is still pending data.
    *
    * The following code uses `Process.start` to grep for `main` in the
    * file `test.dart` on Linux.
    *
    *     Process.start('grep', ['-i', 'main', 'test.dart']).then((process) {
    *       stdout.addStream(process.stdout);
    *       stderr.addStream(process.stderr);
    *     });
+   *
+   * If [detach] is `true` a detached process will be created. A
+   * detached process has no connection to its parent, and can
+   * keep running on its own when the parent dies. The only
+   * information available from a detached process is its `pid`. There
+   * is no connection to its `stdin`, `stdout` or `stderr` nor will its
+   * exit code become available when it terminates.
    */
   external static Future<Process> start(
       String executable,
       List<String> arguments,
       {String workingDirectory,
        Map<String, String> environment,
        bool includeParentEnvironment: true,
-       bool runInShell: false});
+       bool runInShell: false,
+       bool detach: false});
 
   /**
    * Starts a process and runs it non-interactively to completion. The
    * process run is [executable] with the specified [arguments].
    *
    * Use [workingDirectory] to set the working directory for the process. Note
    * that the change of directory occurs before executing the process on some
    * platforms, which may have impact when using relative paths for the
    * executable and the arguments.
    *
@@ skipping 235 matching lines @@
   final int errorCode;
 
   const ProcessException(this.executable, this.arguments, [this.message = "",
                          this.errorCode = 0]);
   String toString() {
     var msg = (message == null) ? 'OS error code: $errorCode' : message;
     var args = arguments.join(' ');
     return "ProcessException: $msg\n  Command: $executable $args";
   }
 }