Add method flush to output stream

runtime/bin/list_stream_impl.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.
 
 /**
  * Default implementation of [ListInputStream].
  */
 class _ListInputStream extends _BaseDataInputStream implements ListInputStream {
   _ListInputStream() : _bufferList = new _BufferList();
 
@@ skipping 46 matching lines @@
     return true;
   }
 
   bool writeFrom(List<int> buffer, [int offset = 0, int len]) {
     if (_streamMarkedClosed) throw new StreamException.streamClosed();
     _bufferList.add(
         buffer.getRange(offset, (len == null) ? buffer.length - offset : len));
     return true;
   }
 
+  void flush() {
+    // Nothing to do on a list output stream.
+  }
+
   void close() {
     if (_streamMarkedClosed) throw new StreamException.streamClosed();
     _streamMarkedClosed = true;
   }
 
   void destroy() {
     close();
   }
 
   void set onNoPendingWrites(void callback()) {
@@ skipping 44 matching lines @@
   }
 
   _BufferList _bufferList;
   bool _streamMarkedClosed = false;
   bool _closeCallbackCalled = false;
   Timer _scheduledNoPendingWriteCallback;
   Timer _scheduledCloseCallback;
   Function _clientNoPendingWriteHandler;
   Function _clientCloseHandler;
 }