Introduce (private) ZLibFilter to dart:io.

runtime/dart-runtime.gyp

 # Copyright (c) 2011, 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.
 
 {
   'includes': [
     'vm/vm.gypi',
     'bin/bin.gypi',
     'third_party/double-conversion/src/double-conversion.gypi',
     'third_party/jscre/jscre.gypi',
+    'third_party/zlib/zlib.gypi',
     'tools/gyp/runtime-configurations.gypi',
     '../tools/gyp/source_filter.gypi',
   ],
   'variables': {
     'version_in_cc_file': 'vm/version_in.cc',
     'version_cc_file': '<(SHARED_INTERMEDIATE_DIR)/version.cc',
   },
   'targets': [
     {
       'target_name': 'libdart',
@@ skipping 73 matching lines @@
             'tools/make_version.py',
             '--output', '<(version_cc_file)',
             '--input', '<(version_in_cc_file)',
             '--version', '../tools/VERSION',
           ],
         },
       ],
     },
   ],
 }