Remove erroneous assert from dart:io's File class.

runtime/bin/file_impl.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 _FileInputStream extends _BaseDataInputStream implements InputStream {
   _FileInputStream(String name)
       : _data = [],
         _position = 0,
         _filePosition = 0 {
     var file = new File(name);
@@ skipping 21 matching lines @@
     });
     chained.handleException((e) {
       _reportError(e);
       return true;
     });
     chained.then((ignored) => _checkScheduleCallbacks());
   }
 
   Future<int> _fillBuffer() {
     Expect.equals(_position, _data.length);
-    Expect.isTrue(_filePosition < _fileLength);
 
     int size = Math.min(_bufferLength, _fileLength - _filePosition);
+    if (size == 0) {
+      _streamMarkedClosed = true;
+      _openedFile.close();
+      return new Future.immediate(0);
+    }
     if (_data.length != size) {
       _data = new Uint8List(size);
     }
     var future = _openedFile.readList(_data, 0, _data.length);
     future = future.transform((read) {
       _filePosition += read;
       if (read != _data.length) {
         _data.removeRange(read, _data.length - read);
       }
       _position = 0;
@@ skipping 1040 matching lines @@
           new FileIOException("File closed '$_name'"));
     });
     return completer.future;
   }
 
   final String _name;
   int _id;
 
   SendPort _fileService;
 }