Switch from interfaces to abstract classes in dart:io.

runtime/bin/chunked_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.
 
 class _ChunkedInputStream implements ChunkedInputStream {
-  _ChunkedInputStream(InputStream this._input, [int chunkSize])
-      : _chunkSize = chunkSize, _bufferList = new _BufferList() {
-    if (_chunkSize === null) {
-      _chunkSize = 0;
-    }
+  _ChunkedInputStream(InputStream this._input, int this._chunkSize)
+      : _bufferList = new _BufferList() {
     _input.onClosed = _onClosed;
   }
 
   List<int> read() {
     if (_closed) return null;
     var result = _bufferList.readBytes(_chunkSize);
     if (result == null) {
       _readData();
       result = _bufferList.readBytes(_chunkSize);
     }
@@ skipping 111 matching lines @@
   InputStream _input;
   _BufferList _bufferList;
   int _chunkSize;
   bool _inputClosed = false;  // Is the underlying input stream closed?
   bool _closed = false;  // Has the close handler been called?.
   Timer _scheduledDataCallback;
   Timer _scheduledCloseCallback;
   Function _clientDataHandler;
   Function _clientCloseHandler;
 }