Fix HttpResponse::writeCharCode.

tests/standalone/io/http_server_response_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 "package:expect/expect.dart";
@@ skipping 270 matching lines @@
       value += 'a';
     }
     request.response.headers.set('name', value);
     request.response.close().catchError((error) {
       server.close();
     }, test: (e) => e is HttpException);
   });
 }
 
 
+void testWriteCharCode() {
+  testServerRequest((server, request) {
+    // Test that default is latin-1 (only 2 bytes).
+    request.response.writeCharCode(0xFF);
+    request.response.writeCharCode(0xFF);
+    request.response.close().then((_) {
+      server.close();
+    });
+  }, bytes: 2);
+}
+
+
 void main() {
   testResponseDone();
   testResponseAddStream();
   testResponseAddStreamClosed();
   testResponseAddClosed();
   testBadResponseAdd();
   testBadResponseClose();
   testIgnoreRequestData();
   testBadHeaders();
+  testWriteCharCode();
 }