Remove Expect from core library.

sdk/lib/io/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.
 
 part of dart.io;
 
 class _FileInputStream extends _BaseDataInputStream implements InputStream {
   _FileInputStream(String name)
       : _data = const [],
         _position = 0,
@@ skipping 41 matching lines @@
     if (available() == 0) _cancelScheduledDataCallback();
     if (!_openedFile.closed) {
       _openedFile.close().then((ignore) {
         _streamMarkedClosed = true;
         _checkScheduleCallbacks();
       });
     }
   }
 
   void _fillBuffer() {
-    Expect.equals(_position, _data.length);
+    assert(_position == _data.length);
     if (_openedFile == null) return;  // Called before the file is opened.
     int size = min(_bufferLength, _fileLength - _filePosition);
     if (size == 0) {
       _closeFile();
       return;
     }
     // If there is currently a _fillBuffer call waiting on read,
     // let it fill the buffer instead of us.
     if (_activeFillBufferCall) return;
     _activeFillBufferCall = true;
@@ skipping 1083 matching lines @@
           new FileIOException("File closed '$_name'"));
     });
     return completer.future;
   }
 
   final String _name;
   int _id;
 
   SendPort _fileService;
 }