Remove deprecated StringBuffer.add, addAll and addCharCode.

pkg/scheduled_test/lib/src/descriptor/utils.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.
 
 library descriptor.utils;
 
 import 'dart:io';
 
 import 'package:pathos/path.dart' as path;
 
@@ skipping 30 matching lines @@
     return matchingEntries.first;
   }
 }
 
 /// Returns a human-readable description of [pattern].
 String describePattern(Pattern pattern) {
   if (pattern is String) return "'$pattern'";
   if (pattern is! RegExp) return '$pattern';
 
   var flags = new StringBuffer();
-  if (!pattern.isCaseSensitive) flags.add('i');
-  if (pattern.isMultiLine) flags.add('m');
+  if (!pattern.isCaseSensitive) flags.write('i');
+  if (pattern.isMultiLine) flags.write('m');
   return '/${pattern.pattern}/$flags';
 }