Uses a finalizer to delete zlib filter resources

sdk/lib/io/data_transformer.dart

Index: sdk/lib/io/data_transformer.dart
diff --git a/sdk/lib/io/data_transformer.dart b/sdk/lib/io/data_transformer.dart
index 144234db92017a8573beb36761ca3fb7b0b10c6c..d3648e786f88176e17db496a0157d1534908a61d 100644
--- a/sdk/lib/io/data_transformer.dart
+++ b/sdk/lib/io/data_transformer.dart
@@ -518,7 +518,6 @@ class _FilterSink extends ByteConversionSink {
       _closed = true;
       throw e;
     }
-    if (!_closed) _filter.end();
     _closed = true;
     _sink.close();
   }
@@ -545,13 +544,6 @@ abstract class _Filter {
    */
   List<int> processed({bool flush: true, bool end: false});
 
-  /**
-   * 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();
-
   external static _Filter _newZLibDeflateFilter(bool gzip, int level,
                                                 int windowBits, int memLevel,
                                                 int strategy,