Add support for killing a process with a given PID to dart:io

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 328 matching lines @@
       String executable,
       List<String> arguments,
       {String workingDirectory,
        Map<String, String> environment,
        bool includeParentEnvironment: true,
        bool runInShell: false,
        Encoding stdoutEncoding: SYSTEM_ENCODING,
        Encoding stderrEncoding: SYSTEM_ENCODING});
 
   /**
+   * On Linux and Mac OS, [killPid] sends [signal] to the process with

[Lasse Reichstein Nielsen, 2015/02/03 14:00:47]

Is it officially called Mac OS? Or is it just OS X? (Wikipedia says it was
renamed to just OS X in 2012)

[Søren Gjesse, 2015/02/04 08:16:02]

You are right. We are currently using Mac OS in the other files in the SDK, but
there are < 20 occurrences. I will change it here and make a CL for changing the
rest.

+   * process id [pid].
+   *
+   * On Windows, `killPid` kills the process with process `pid` , ignoring the
+   * `signal` flag.

[Lasse Reichstein Nielsen, 2015/02/03 14:00:47]

Start with a single statement describing the operation with no conditionals or
details, e.g.:
  Kills the process with id `pid`.
Then heap on the details. If a summary of the API only shows the first line,
then it might look like this function only works on OS/X and Linux.

This restricts us to those three three OSes (which is probably not just
happening here).

Could it be written as:

Where possible, sends the [signal] to the process with id [pid]. This includes
Linux and OS/X. The default signal is [ProcessSignal.SIGTERM] which will
terminate the process.

On platforms without signal support, including Windows, the call just kills the
process with id `pid` in a platform specific way, and the 
`signal` parameter is ignored.

Can't you send signals on Windows?
https://msdn.microsoft.com/en-us/library/ms811896.aspx#ucmgch09_topic3

[Søren Gjesse, 2015/02/04 08:16:02]

Thanks, rewritten.

The signals you can receive on Windows are only exceptions generated by the OS,
and cannot be send from another process through an API.

+   *
+   * Returns `true` if the signal is successfully sent and process is killed.

[Lasse Reichstein Nielsen, 2015/02/03 14:00:47]

and process -> and the process

What if the process intercepts the SIGTERM signal? Does it return true in that
case (I guess yes), but the process isn't killed.

SO:
  Returns `true` if the signal is successfully sent.
but skip" process is killed" because it might not be.

[Søren Gjesse, 2015/02/04 08:16:02]

You are right. We can only see if the signal was send.

+   * Otherwise the signal could not be sent, usually meaning that the process is
+   * already dead.
+   */
+  external static bool killPid(
+      int pid, [ProcessSignal signal = ProcessSignal.SIGTERM]);
+
+  /**
    * Returns the standard output stream of the process as a [:Stream:].
    */
   Stream<List<int>> get stdout;
 
   /**
    * Returns the standard error stream of the process as a [:Stream:].
    */
   Stream<List<int>> get stderr;
 
   /**
@@ skipping 162 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";
   }
 }