Reapply "Update the test runner to use the new dart:io API"

tools/testing/dart/test_options.dart

-// Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
+// 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.
 
 library test_options_parser;
 
 import "dart:io";
 import "dart:math";
 import "drt_updater.dart";
 import "test_suite.dart";
 
@@ skipping 636 matching lines @@
    * Print out usage information.
    */
   void _printHelp() {
     print('usage: dart test.dart [options]\n');
     print('Options:\n');
     for (var option in _options) {
       print('${option.name}: ${option.description}.');
       for (var name in option.keys) {
         assert(name.startsWith('-'));
         var buffer = new StringBuffer();;
-        buffer.add(name);
+        buffer.write(name);
         if (option.type == 'bool') {
           assert(option.values.isEmpty);
         } else {
-          buffer.add(name.startsWith('--') ? '=' : ' ');
+          buffer.write(name.startsWith('--') ? '=' : ' ');
           if (option.type == 'int') {
             assert(option.values.isEmpty);
-            buffer.add('n (default: ${option.defaultValue})');
+            buffer.write('n (default: ${option.defaultValue})');
           } else {
-            buffer.add('[');
+            buffer.write('[');
             bool first = true;
             for (var value in option.values) {
-              if (!first) buffer.add(", ");
-              if (value == option.defaultValue) buffer.add('*');
-              buffer.add(value);
+              if (!first) buffer.write(", ");
+              if (value == option.defaultValue) buffer.write('*');
+              buffer.write(value);
               first = false;
             }
-            buffer.add(']');
+            buffer.write(']');
           }
         }
         print(buffer.toString());
       }
       print('');
     }
   }
 
 
   /**
    * Find the test option specification for a given option key.
    */
   _TestOptionSpecification _getSpecification(String name) {
     for (var option in _options) {
       if (option.keys.any((key) => key == name)) {
         return option;
       }
     }
     print('Unknown test option $name');
     exit(1);
   }
 
 
   List<_TestOptionSpecification> _options;
 }