Switch from interfaces to abstract classes in dart:io.

runtime/bin/output_stream.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.
 
 /**
  * Output streams are used to write data sequentially to a data
  * destination e.g. a connected socket or an open file.
  *
  * An output stream provides internal buffering of the data written
  * through all calls to [write] and [writeFrom] if data cannot be
  * written immediately to the communication channel. The callback set
  * through [onNoPendingWrites] can be used to to keep the rate of
  * writing in sync with the rate the system can actually write data to
  * the underlying communication channel.
  */
-interface OutputStream {
+abstract class OutputStream {
   /**
    * Writes the content of [buffer] to the stream. If [copyBuffer] is
    * false ownership of the specified buffer is passed to the system
    * and the caller should not change it afterwards. The default value
    * for [copyBuffer] is true.
    *
    * Returns true if the data could be written to the underlying
    * communication channel immediately. Otherwise the data is buffered
    * by the output stream and will be sent as soon as possible.
    */
@@ skipping 65 matching lines @@
    */
   void set onClosed(void callback());
 
   /**
    * Sets the handler that gets called when the underlying
    * communication channel gets into some kind of error situation.
    */
   void set onError(void callback(e));
 }