Update ZLib/GZip in dart:io to be a Codec/Converter from dart:convert.

sdk/lib/io/http_impl.dart

Index: sdk/lib/io/http_impl.dart
diff --git a/sdk/lib/io/http_impl.dart b/sdk/lib/io/http_impl.dart
index 7eaf153f32f879ecb7e82a556766b7bf0448e542..f7b904122793fe3dc6455a7fd190d9a545b05824 100644
--- a/sdk/lib/io/http_impl.dart
+++ b/sdk/lib/io/http_impl.dart
@@ -243,7 +243,7 @@ class _HttpClientResponse
                                         bool cancelOnError}) {
     var stream = _incoming;
     if (headers.value(HttpHeaders.CONTENT_ENCODING) == "gzip") {
-      stream = stream.transform(new ZLibInflater());
+      stream = stream.transform(GZIP.decoder);
     }
     return stream.listen(onData,
                          onError: onError,
@@ -516,7 +516,7 @@ abstract class _HttpOutboundMessage<T> implements IOSink {
           stream = stream.transform(new _BufferTransformer());
           if (headers.chunkedTransferEncoding) {
             if (_asGZip) {
-              stream = stream.transform(new ZLibDeflater(gzip: true, level: 6));
+              stream = stream.transform(GZIP.encoder);
             }
             stream = stream.transform(new _ChunkedTransformer());
           } else if (contentLength >= 0) {