Introduce (private) ZLibFilter to dart:io.

runtime/bin/filter.dart

Index: runtime/bin/filter.dart
diff --git a/tests/compiler/dart2js_extra/source_mapping_crash_test.dart b/runtime/bin/filter.dart
similarity index 53%
copy from tests/compiler/dart2js_extra/source_mapping_crash_test.dart
copy to runtime/bin/filter.dart
index 63b038ec3038599b030949ff01ce4b15363299d1..59ceb2b64e4edd1e4108a6003d0bb080b2e18440 100644
--- a/tests/compiler/dart2js_extra/source_mapping_crash_test.dart
+++ b/runtime/bin/filter.dart
@@ -2,16 +2,15 @@
 // 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.
 
-#library('source_mapping_crash_test');
 
-#source('source_mapping_crash_source.dart');
+abstract class Filter {
+  Future<List<int>> process(List<int> data);
 
-class Sub extends Super {
-  Sub(var x) : super(x.y);
+  // FIXME: Rename to 'done'?
+  void end();
 }
 
-class X { var y; }
-
-main() {
-  new Sub(new X());
+class ZLibFilter implements Filter {
+  factory ZLibFilter() => new _ZLibFilterImpl();
 }
+