Make stdout and stderr async.

runtime/bin/eventhandler.h

 // 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.
 
 #ifndef BIN_EVENTHANDLER_H_
 #define BIN_EVENTHANDLER_H_
 
 #include "bin/builtin.h"
 #include "bin/isolate_data.h"
 
@@ skipping 101 matching lines @@
    * Start the event-handler.
    */
   static void Start();
 
   /**
    * Stop the event-handler. It's expected that there will be no further calls
    * to SendData after a call to Stop.
    */
   static void Stop();
 
+  static EventHandlerImplementation* delegate();
+
  private:
   friend class EventHandlerImplementation;
   EventHandlerImplementation delegate_;
 };
 
 }  // namespace bin
 }  // namespace dart
 
 #endif  // BIN_EVENTHANDLER_H_