Introduce (private) ZLibFilter to dart:io.

runtime/bin/filter.h

+// 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.
+
+#ifndef BIN_FILTER_H_
+#define BIN_FILTER_H_
+
+#include "bin/builtin.h"
+#include "bin/utils.h"
+
+
+class Filter {
+ protected:
+  Filter() {}
+  virtual ~Filter() {}
+
+ public:
+  virtual bool Init() = 0;
+  virtual uint8_t* Process(uint8_t* data,
+                           intptr_t length,
+                           intptr_t& outputLength) = 0;
+
+ public:
+  static Dart_Handle SetFilterPointerNativeField(Dart_Handle filter,
+                                                 Filter* filter_pointer);
+  static Dart_Handle GetFilterPointerNativeField(Dart_Handle filter,
+                                                 Filter** filter_pointer);
+};
+
+class ZLibFilter : public Filter {
+ public:
+  virtual ~ZLibFilter();
+
+ public:
+  virtual bool Init();
+  virtual uint8_t* Process(uint8_t* data,
+                           intptr_t length,
+                           intptr_t& outputLength);
+};
+
+#endif  // BIN_FILTER_H_
+