Fix checked mode errors in previous commit

sdk/lib/_internal/compiler/implementation/lib/io_patch.dart

 // Copyright (c) 2013, 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.
 
 patch class _BufferUtils {
   patch static bool _isBuiltinList(List buffer) {
     throw new UnsupportedError("_isBuiltinList");
   }
 }
 
 patch class _Directory {
   patch static String _current() {
     throw new UnsupportedError("Directory._current");
   }
-  patch static _setCurrent(String path) {
+  patch static _setCurrent(path) {
     throw new UnsupportedError("Directory_SetCurrent");
   }
   patch static _createTemp(String template) {
     throw new UnsupportedError("Directory._createTemp");
   }
   patch static int _exists(String path) {
     throw new UnsupportedError("Directory._exists");
   }
   patch static _create(String path) {
     throw new UnsupportedError("Directory._create");
@@ skipping 245 matching lines @@
 }
 
 patch class _Filter {
   patch static _Filter newZLibDeflateFilter(bool gzip, int level) {
     throw new UnsupportedError("newZLibDeflateFilter");
   }
   patch static _Filter newZLibInflateFilter() {
     throw new UnsupportedError("newZLibInflateFilter");
   }
 }