Add writeString method to OutputStream

runtime/bin/stream_util.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.
 
 class _BaseDataInputStream {
   abstract int available();
 
   List<int> read([int len]) {
     if (_closeCallbackCalled) return null;
     int bytesToRead = available();
@@ skipping 157 matching lines @@
     input.onData = pipeDataHandler;
     output.onNoPendingWrites = null;
   };
 
   _inputCloseHandler = input._clientCloseHandler;
   input.onData = pipeDataHandler;
   input.onClosed = pipeCloseHandler;
   output.onNoPendingWrites = null;
 }
 
+
+class _BaseOutputStream {
+  bool writeString(String string, [Encoding encoding = Encoding.UTF_8]) {
+    if (string.length > 0) {
+      // Encode and write data.
+      StringEncoder encoder = _StringEncoders.encoder(encoding);
+      List<int> data = encoder.encodeString(string);
+      return write(data, copyBuffer: false);
+    }
+    return true;
+  }
+}