Remove deprecated StringBuffer.add, addAll and addCharCode.

tests/standalone/io/http_detach_socket_test.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.
 //
 // VMOptions=
 // VMOptions=--short_socket_read
 // VMOptions=--short_socket_write
 // VMOptions=--short_socket_read --short_socket_write
 
 import "dart:io";
 import "dart:isolate";
 
 void testServerDetachSocket() {
   HttpServer.bind().then((server) {
     server.listen((request) {
       var response = request.response;
       response.contentLength = 0;
       response.detachSocket().then((socket) {
         Expect.isNotNull(socket);
         var body = new StringBuffer();
         socket.listen(
-          (data) => body.add(new String.fromCharCodes(data)),
+          (data) => body.write(new String.fromCharCodes(data)),
           onDone: () => Expect.equals("Some data", body.toString()));
         socket.addString("Test!");
         socket.close();
       });
       server.close();
     });
 
     Socket.connect("127.0.0.1", server.port).then((socket) {
       socket.addString("GET / HTTP/1.1\r\n"
                        "content-length: 0\r\n\r\n"
                        "Some data");
       var body = new StringBuffer();
       socket.listen(
-        (data) => body.add(new String.fromCharCodes(data)),
+        (data) => body.write(new String.fromCharCodes(data)),
         onDone: () {
           Expect.equals("HTTP/1.1 200 OK\r\n"
                         "content-length: 0\r\n"
                         "\r\n"
                         "Test!",
                         body.toString());
           socket.close();
         });
     });
   });
@@ skipping 20 matching lines @@
 }
 
 void testClientDetachSocket() {
   ServerSocket.bind().then((server) {
     server.listen((socket) {
       socket.addString("HTTP/1.1 200 OK\r\n"
                        "\r\n"
                        "Test!");
       var body = new StringBuffer();
       socket.listen(
-        (data) => body.add(new String.fromCharCodes(data)),
+        (data) => body.write(new String.fromCharCodes(data)),
         onDone: () {
           Expect.equals("GET / HTTP/1.1\r\n"
                         "content-length: 0\r\n"
                         "host: 127.0.0.1:${server.port}\r\n\r\n"
                         "Some data",
                         body.toString());
           socket.close();
         });
       server.close();
     });
 
     var client = new HttpClient();
     client.get("127.0.0.1", server.port, "/")
       .then((request) => request.close())
       .then((response) {
         response.detachSocket().then((socket) {
           var body = new StringBuffer();
           socket.listen(
-            (data) => body.add(new String.fromCharCodes(data)),
+            (data) => body.write(new String.fromCharCodes(data)),
             onDone: () {
               Expect.equals("Test!",
                             body.toString());
               client.close();
             });
           socket.addString("Some data");
           socket.close();
         });
       });
   });
 }
 
 void main() {
   testServerDetachSocket();
   testBadServerDetachSocket();
   testClientDetachSocket();
 }