Work around a VM crash, with Stdout.

sdk/lib/io/stdio.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.
 
 part of dart.io;
 
 const int _STDIO_HANDLE_TYPE_TERMINAL = 0;
 const int _STDIO_HANDLE_TYPE_PIPE = 1;
 const int _STDIO_HANDLE_TYPE_FILE = 2;
 const int _STDIO_HANDLE_TYPE_SOCKET = 3;
@@ skipping 146 matching lines @@
    */
   external int readByteSync();
 }
 
 
 /**
  * [Stdout] exposes methods to query the terminal for properties.
  *
  * Use [hasTerminal] to test if there is a terminal associated to stdout.
  */
-class Stdout extends _StdSink implements IOSink {
+class Stdout extends _StdSink {
+  // TODO(15721): Should implement IOSink (for documentation purpose).
   Stdout._(IOSink sink) : super(sink);
 
   /**
    * Returns true if there is a terminal attached to stdout.
    */
   external bool get hasTerminal;
 
   /**
    * Get the number of columns of the terminal.
    *
@@ skipping 119 matching lines @@
   }
   return StdioType.OTHER;
 }
 
 
 class _StdIOUtils {
   external static _getStdioOutputStream(int fd);
   external static Stdin _getStdioInputStream();
   external static int _socketType(nativeSocket);
 }