a === b -> identical(a, b)

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.
 
 class _FileInputStream extends _BaseDataInputStream implements InputStream {
   _FileInputStream(String name)
       : _data = const [],
         _position = 0,
         _filePosition = 0 {
     var file = new File(name);
@@ skipping 231 matching lines @@
     }
   }
 
   void set onClosed(void callback()) {
     _onClosed = callback;
   }
 
   void _processPendingOperations() {
     _pendingOperations.forEach((buffer) {
       if (buffer is _PendingOperation) {
-        if (buffer === _PendingOperation.CLOSE) {
+        if (identical(buffer, _PendingOperation.CLOSE)) {
           close();
         } else {
-          assert(buffer === _PendingOperation.FLUSH);
+          assert(identical(buffer, _PendingOperation.FLUSH));
           flush();
         }
       } else {
         write(buffer);
       }
     });
     _pendingOperations = null;
   }
 
   void _write(List<int> buffer, int offset, int len) {
@@ skipping 814 matching lines @@
           new FileIOException("File closed '$_name'"));
     });
     return completer.future;
   }
 
   final String _name;
   int _id;
 
   SendPort _fileService;
 }