Turn on dartc testing of tests/standalone.

tests/standalone/io/process_test_util.dart

 // Copyright (c) 2012, 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.
 
+library process_test_util;
+
+import "dart:io";
+
 String getPlatformExecutableExtension() {
   var os = Platform.operatingSystem;
   if (os == 'windows') return '.exe';
   return '';  // Linux and Mac OS.
 }
 
 String getProcessTestFileName() {
   var extension = getPlatformExecutableExtension();
   var executable = new Options().executable;
   var dirIndex = executable.lastIndexOf('dart$extension');
   var buffer = new StringBuffer(executable.substring(0, dirIndex));
   buffer.add('process_test$extension');
   return buffer.toString();
 }