Introduce (private) ZLibFilter to dart:io.

runtime/bin/filter.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.
+
+
+abstract class _Filter {
+  /**
+   * Call to process a chunk of data. A call to [process] should only be made
+   * when [processed] returns [null].
+   */
+  void process(List<int> data);
+
+  /**
+   * Get a chunk of processed data. When there are no more data available,
+   * [processed] will return [null]. Set [flush] to [false] for non-final
+   * calls to improve performance of some filters.
+   */
+  List<int> processed([bool flush = true]);
+
+  /**
+   * Mark the filter as closed. Always call this method for any filter created
+   * to avoid leaking resources. [end] can be called at any time, but any
+   * successive calls to [process] or [processed] will fail.
+   */
+  void end();
+}
+
+class GZipDeflateFilter implements _Filter {
+  factory GZipDeflateFilter()
+    => new _GZipDeflateFilterImpl();
+}
+
+class ZLibInflateFilter implements _Filter {
+  factory ZLibInflateFilter() => new _ZLibInflateFilterImpl();
+}
+