Introduce (private) ZLibFilter to dart:io.

runtime/bin/filter_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 _FilterImpl extends NativeFieldWrapperClass1 implements _Filter {
+  _FilterImpl() {
+    _init();
+  }
+
+  void process(List<int> data) native "Filter_Process";
+
+  List<int> processed([bool flush = false]) native "Filter_Processed";
+
+  void end() native "Filter_End";
+}
+
+class _GZipDeflateFilterImpl extends _FilterImpl {
+  void _init() native "Filter_CreateGZipDeflate";
+}
+
+class _ZLibInflateFilterImpl extends _FilterImpl {
+  void _init() native "Filter_CreateZLibInflate";
+}