Remove usage of dart:utf from dart:io.

sdk/lib/io/websocket_impl.dart

Index: sdk/lib/io/websocket_impl.dart
diff --git a/sdk/lib/io/websocket_impl.dart b/sdk/lib/io/websocket_impl.dart
index aec29197075b7cf80ecc23a3216acd3cfb31cc84..84aa4c90bec967259a75bef900b341d7d9a861ff 100644
--- a/sdk/lib/io/websocket_impl.dart
+++ b/sdk/lib/io/websocket_impl.dart
@@ -95,7 +95,7 @@ class _WebSocketProtocolTransformer extends StreamEventTransformer {
               _currentMessageType = _WebSocketMessageType.TEXT;
               _controller = new StreamController(sync: true);
               _controller.stream
-                  .transform(new Utf8DecoderTransformer(null))
+                  .transform(UTF8.decoder)
                   .fold(new StringBuffer(), (buffer, str) => buffer..write(str))
                   .then((buffer) {
                     sink.add(buffer.toString());
@@ -304,7 +304,7 @@ class _WebSocketProtocolTransformer extends StreamEventTransformer {
             throw new WebSocketException("Protocol error");
           }
           if (_controlPayload.length > 2) {
-            closeReason = _decodeUtf8Strict(_controlPayload.sublist(2));
+            closeReason = UTF8.decode(_controlPayload.sublist(2));
           }
         }
         _state = CLOSED;