Turn on dartc testing of tests/standalone.

tests/standalone/io/process_test_util.dart

Index: tests/standalone/io/process_test_util.dart
diff --git a/tests/standalone/io/process_test_util.dart b/tests/standalone/io/process_test_util.dart
index 61ad729b8240d3207d9c31d6a2f749acf0cad7ae..6abf0c6849e6f71c6ccadc78b232816b33407982 100644
--- a/tests/standalone/io/process_test_util.dart
+++ b/tests/standalone/io/process_test_util.dart
@@ -2,6 +2,10 @@
 // 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.
 
+library process_test_util;
+
+import "dart:io";
+
 String getPlatformExecutableExtension() {
   var os = Platform.operatingSystem;
   if (os == 'windows') return '.exe';