Remove deprecated StringBuffer.add, addAll and addCharCode.

tests/language/field_initialization_order_test.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.
 
 // Test that field initializers are evaluated in the right order.
 
 int counter = 0;
 
 class Mark {
   static StringBuffer buffer;
   Mark(value) {
-    buffer.add('$value.');
+    buffer.write('$value.');
   }
 }
 
 class OneField {
   var a = new Mark('a');
 
   OneField();
 
   OneField.init() : a = new Mark('ai');
 }
@@ skipping 44 matching lines @@
       new InheritOneField()));
   Expect.equals('b.bi.a.', run(() =>
       new InheritOneField.init()));
   Expect.equals('b.a.ai.', run(() =>
       new InheritOneField.superWithInit()));
   Expect.equals('b.bi.a.ai.', run(() =>
       new InheritOneField.initWithSuperInit()));
   Expect.equals('b.a.ai.bi.', run(() =>
       new InheritOneField.initWithSuperInit2()));
 }