Add Directory.systemTemp getter to replace createSystemTemp().

sdk/lib/_internal/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 _Directory {
   patch static _current() {
     throw new UnsupportedError("Directory._current");
   }
   patch static _setCurrent(path) {
     throw new UnsupportedError("Directory_SetCurrent");
   }
-  patch static _createTemp(String template, bool system) {
+  patch static _createTemp(String path) {
     throw new UnsupportedError("Directory._createTemp");
   }
+  patch static String _systemTemp() {
+    throw new UnsupportedError("Directory._systemTemp");
+  }
   patch static int _exists(String path) {
     throw new UnsupportedError("Directory._exists");
   }
   patch static _create(String path) {
     throw new UnsupportedError("Directory._create");
   }
   patch static _deleteNative(String path, bool recursive) {
     throw new UnsupportedError("Directory._deleteNative");
   }
   patch static _rename(String path, String newPath) {
@@ skipping 320 matching lines @@
   patch static bool get isSupported {
     throw new UnsupportedError("_FileSystemWatcher.isSupported");
   }
 }
 
 patch class _IOService {
   patch static Future dispatch(int request, List data) {
     throw new UnsupportedError("_IOService.dispatch");
   }
 }