Use patching for dart:io.

lib/io/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();
+abstract class _BaseDataInputStream {
+  int available();
 
   List<int> read([int len]) {
     if (_closeCallbackCalled || _scheduledCloseCallback != null) return null;
     int bytesToRead = available();
     if (bytesToRead == 0) {
       _checkScheduleCallbacks();
       return null;
     }
     if (len !== null) {
       if (len <= 0) {
@@ skipping 41 matching lines @@
   }
 
   void _reportError(e) {
     if (_clientErrorHandler != null) {
       _clientErrorHandler(e);
     } else {
       throw e;
     }
   }
 
-  abstract List<int> _read(int bytesToRead);
+  List<int> _read(int bytesToRead);
 
   void _dataReceived() {
     // More data has been received asynchronously. Perform the data
     // handler callback now.
     _cancelScheduledDataCallback();
     if (_clientDataHandler !== null) {
       _clientDataHandler();
     }
     _checkScheduleCallbacks();
   }
@@ skipping 121 matching lines @@
   void _reportError(e) {
     if (_onError != null) {
       _onError(e);
     } else {
       throw e;
     }
   }
 
   Function _onError;
 }