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

tests/standalone/io/process_kill_test.dart

Index: tests/standalone/io/process_kill_test.dart
diff --git a/tests/standalone/io/process_kill_test.dart b/tests/standalone/io/process_kill_test.dart
index 673933649893dc9e0a3021218ae8b7cd8be36a9b..4955b2c1782b2379830ce8636b62ce1adbd9a33d 100644
--- a/tests/standalone/io/process_kill_test.dart
+++ b/tests/standalone/io/process_kill_test.dart
@@ -22,6 +22,20 @@ testKill() {
   });
 }
 
+testKillPid() {
+  // Start a process that will hang waiting for input until killed.

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

You need to add startAsync/endAsync calls, otherwise the test succeedes before
it has time to fail.
Same goes for first test.

[Søren Gjesse, 2015/02/04 08:16:02]

Thanks, done.

+  Process.start(getProcessTestFileName(), const ["0", "1", "0", "0"]).then((p) {
+    p.exitCode.then((exitCode) {
+      // Process killed from the side so exit code is not 0.
+      Expect.isTrue(exitCode != 0);
+      // Killing a process that is already dead returns false.
+      Expect.isFalse(p.kill());

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

Why not Process.killPid(p.pid) ?

[Søren Gjesse, 2015/02/04 08:16:02]

Done.

+    });
+    Expect.isTrue(Process.killPid(p.pid));
+  });
+}
+
 main() {
   testKill();
+  testKillPid();
 }