Remove deprecated StringBuffer.add, addAll and addCharCode.

tests/standalone/io/http_basic_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:isolate";
@@ skipping 186 matching lines @@
 void testGET() {
   TestServerMain testServerMain = new TestServerMain();
   testServerMain.setServerStartedHandler((int port) {
     HttpClient httpClient = new HttpClient();
     httpClient.get("127.0.0.1", port, "/0123456789")
         .then((request) => request.close())
         .then((response) {
           Expect.equals(HttpStatus.OK, response.statusCode);
           StringBuffer body = new StringBuffer();
           response.listen(
-            (data) => body.add(new String.fromCharCodes(data)),
+            (data) => body.write(new String.fromCharCodes(data)),
             onDone: () {
               Expect.equals("01234567890", body.toString());
               httpClient.close();
               testServerMain.close();
             });
         });
   });
   testServerMain.start();
 }
 
@@ skipping 15 matching lines @@
             } else {
               request.contentLength = data.length;
               request.addString(data);
             }
             return request.close();
           })
           .then((response) {
             Expect.equals(HttpStatus.OK, response.statusCode);
             StringBuffer body = new StringBuffer();
             response.listen(
-              (data) => body.add(new String.fromCharCodes(data)),
+              (data) => body.write(new String.fromCharCodes(data)),
               onDone: () {
                 Expect.equals(data, body.toString());
                 count++;
                 if (count < kMessageCount) {
                   sendRequest();
                 } else {
                   httpClient.close();
                   testServerMain.close();
                 }
               });
@@ skipping 13 matching lines @@
 void test404() {
   TestServerMain testServerMain = new TestServerMain();
   testServerMain.setServerStartedHandler((int port) {
     HttpClient httpClient = new HttpClient();
     httpClient.get("127.0.0.1", port, "/thisisnotfound")
         .then((request) => request.close())
         .then((response) {
           Expect.equals(HttpStatus.NOT_FOUND, response.statusCode);
           var body = new StringBuffer();
           response.listen(
-              (data) => body.add(new String.fromCharCodes(data)),
+              (data) => body.write(new String.fromCharCodes(data)),
               onDone: () {
                 Expect.equals("Page not found", body.toString());
                 httpClient.close();
                 testServerMain.close();
               });
         });
   });
   testServerMain.start();
 }
 
@@ skipping 22 matching lines @@
 }
 
 void main() {
   testStartStop();
   testGET();
   testPOST(true);
   testPOST(false);
   test404();
   testReasonPhrase();
 }