Add writeString method to OutputStream

tests/standalone/src/io/ListOutputStreamTest.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.
 
 #import("dart:io");
 #import("dart:isolate");
 
 void testEmptyListOutputStream1() {
   OutputStream stream = new ListOutputStream();
   Expect.equals(null, stream.contents());
@@ skipping 67 matching lines @@
     Expect.equals(null, stream.contents());
     donePort.toSendPort().send(null);
   }
 
   stream.onNoPendingWrites = onNoPendingWrites;
   stream.onClosed = onClosed;
 
   donePort.receive((x,y) => donePort.close());
 }
 
+void testListOutputStream3() {
+  OutputStream stream = new ListOutputStream();
+  ReceivePort donePort = new ReceivePort();
+  void onNoPendingWrites() {
+    stream.writeString("abcdABCD");
+    stream.writeString("abcdABCD", Encoding.UTF_8);
+    stream.writeString("abcdABCD", Encoding.ISO_8859_1);
+    stream.writeString("abcdABCD", Encoding.ASCII);
+    stream.writeString("æøå", Encoding.UTF_8);
+    stream.close();
+  }
+
+  void onClosed() {
+    var contents = stream.contents();
+    Expect.equals(38, contents.length);
+    donePort.toSendPort().send(null);
+  }
+
+  stream.onNoPendingWrites = onNoPendingWrites;
+  stream.onClosed = onClosed;
+
+  donePort.receive((x,y) => donePort.close());
+}
+
 main() {
   testEmptyListOutputStream1();
   testEmptyListOutputStream2();
   testListOutputStream1();
   testListOutputStream2();
+  testListOutputStream3();
 }