Make IOSink implement StringSink

tests/standalone/io/stream_pipe_test.dart

-// Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
+// 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
 library ServerTest;
 
 import "dart:io";
@@ skipping 81 matching lines @@
       getDataFilename("tests/standalone/io/readline_test1.dat");
   var srcFile = new File(srcFileName);
   var srcStream = srcFile.openRead();
 
   var tempDir = new Directory('').createTempSync();
   var dstFileName = tempDir.path.concat("/readline_test1.dat");
   var dstFile = new File(dstFileName);
   dstFile.createSync();
   var output = dstFile.openWrite();
   output.addStream(srcStream).then((_) {
-    output.add([32]);
+    output.writeBytes([32]);
     output.close();
     output.done.then((_) {
       var src = srcFile.openSync();
       var dst = dstFile.openSync();
       var srcLength = src.lengthSync();
       var dstLength = dst.lengthSync();
       Expect.equals(srcLength + 1, dstLength);
       Expect.isTrue(compareFileContent(srcFileName,
                                        dstFileName,
                                        count: srcLength));
@@ skipping 54 matching lines @@
     });
   });
 }
 
 
 main() {
   testFileToFilePipe1();
   testFileToFilePipe2();
   testFileToFilePipe3();
 }