Don't close stdio/stderr when shutting down.

tests/standalone/io/stdio_implicit_close_test.dart

+// Copyright (c) 2013, 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.
+
+import "package:async_helper/async_helper.dart";
+import "package:expect/expect.dart";
+import "dart:convert";
+import "dart:io";
+
+void test({bool closeStdout, bool closeStderr}) {
+  var scriptFile = "stdio_implicit_close_script.dart";
+  var script = Platform.script.resolve(scriptFile).toFilePath();
+
+  // Relying on these flags to print something specific on stdout and stderr
+  // is brittle, but otherwise we would need to add our own flag.
+  var arguments = [
+      "--print-metrics",  // Prints on stderr.
+      "--timing",         // Prints on stdout.
+      script,
+  ];
+  if (closeStdout) arguments.add("stdout");
+  if (closeStderr) arguments.add("stderr");
+
+  asyncStart();
+  Process.run(Platform.executable,
+              arguments,
+              stdoutEncoding: ASCII,
+              stderrEncoding: ASCII).then((result) {
+                  print(result.stdout);
+                  print(result.stderr);
+    Expect.equals(0, result.exitCode);
+
+    if (closeStdout) {
+      Expect.equals("", result.stdout);
+    } else {
+      Expect.isTrue(result.stdout.contains("Timing for"));
+    }
+
+    if (closeStderr) {
+      Expect.equals("", result.stderr);
+    } else {
+      Expect.isTrue(result.stderr.contains("Printing metrics"));
+    }
+
+    asyncEnd();
+  });
+}
+
+void main() {
+  asyncStart();
+  test(closeStdout: false, closeStderr: false);
+  test(closeStdout: false, closeStderr: true);
+  test(closeStdout: true, closeStderr: false);
+  test(closeStdout: true, closeStderr: true);
+  asyncEnd();
+}