Use SIGKILL in regress_7191_script.

tests/standalone/io/regress_7191_script.dart

Index: tests/standalone/io/regress_7191_script.dart
diff --git a/tests/standalone/io/regress_7191_script.dart b/tests/standalone/io/regress_7191_script.dart
index 9f7c78036973524873fabcdde652c631a4f494a6..9f6a346308146c355333d08e704e65bd7edb8460 100644
--- a/tests/standalone/io/regress_7191_script.dart
+++ b/tests/standalone/io/regress_7191_script.dart
@@ -16,7 +16,10 @@ main() {
       p.stderr.listen((_) { });
       // When receiving data again, kill sub-process and exit.
       subscription.onData((data) {
-        p.kill();
+        // If a SIGTERM is sent before the child-process's main is invoked,
+        // there is a change that the SIGTERM is ignore on Mac OS X. Use
+        // SIGKILL to get around the issue.
+        p.kill(ProcessSignal.SIGKILL);
         p.exitCode.then((_) => exit(0));
       });
       // Close stdout. If handles are incorrectly inherited this will