Remove deprecated StringBuffer.add, addAll and addCharCode.

tests/standalone/io/file_input_stream_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.
 // Testing file input stream, VM-only, standalone test.
 
 import "dart:io";
 import "dart:isolate";
 
 // Helper method to be able to run the test from the runtime
 // directory, or the top directory.
@@ skipping 35 matching lines @@
       });
 }
 
 
 // Create a file that is big enough that a file stream will
 // read it in multiple chunks.
 int writeLongFileSync(File file) {
   file.createSync();
   StringBuffer buffer = new StringBuffer();
   for (var i = 0; i < 10000; i++) {
-    buffer.add("Hello, world");
+    buffer.write("Hello, world");
   }
   file.writeAsStringSync(buffer.toString());
   var length = file.lengthSync();
   Expect.equals(buffer.length, length);
   return length;
 }
 
 
 void testInputStreamTruncate() {
   var keepAlive = new ReceivePort();
@@ skipping 129 matching lines @@
   testOpenStreamAsync();
   testInputStreamTruncate();
   testInputStreamDelete();
   testInputStreamAppend();
   // Check the length of these files as both are text files where one
   // is without a terminating line separator which can easily be added
   // back if accidentally opened in a text editor.
   testStringLineTransformerEnding("readline_test1.dat", 111);
   testStringLineTransformerEnding("readline_test2.dat", 114);
 }