Fix running tests with --checked

runtime/bin/chunked_stream.dart

 // Copyright (c) 2011, 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;
     }
@@ skipping 47 matching lines @@
 
   void _readData() {
     List<int> data = _input.read();
     if (data !== null) {
       _bufferList.add(data);
     }
   }
 
   void _closeHandler() {
     _inputClosed = true;
-    if (_bufferList.length == 0 && _clientCloseHandler) {
+    if (_bufferList.length == 0 && _clientCloseHandler !== null) {
       _clientCloseHandler();
       _closed = true;
     } else {
       _checkScheduleCallback();
     }
   }
 
   void _checkInstallDataHandler() {
     if (_clientDataHandler === null) {
       _input.dataHandler = null;
@@ skipping 37 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?.
   var _clientDataHandler;
   var _clientCloseHandler;
 }