Remove deprecated StringBuffer.add, addAll and addCharCode.

tests/language/final_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 initializers for final fields are evaluated in the right
 // order.
 
 int counter = 0;
 
 class Mark {
   static StringBuffer buffer;
   Mark(value) {
-    buffer.add('$value.');
+    buffer.write('$value.');
   }
 }
 
 class OneField {
   final a = new Mark('a');
   OneField();
 }
 
 class TwoFields {
   final a = new Mark('a');
@@ skipping 25 matching lines @@
 main() {
   Expect.equals('a.', run(() => new OneField()));
   Expect.equals('a.b.', run(() => new TwoFields()));
   Expect.equals('b.a.', run(() => new InheritOneField()));
 
   Expect.equals('b.c.d.a.', run(() => new MixedFields()));
   Expect.equals('b.c.d.cc.a.', run(() => new MixedFields.c0()));
   Expect.equals('b.c.d.cc.a.', run(() => new MixedFields.c1()));
   Expect.equals('b.c.d.a.cc.', run(() => new MixedFields.c2()));
 }