Modify tests to use Directory.systemTemp

tests/standalone/io/file_fuzz_test.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.
 
 // 'fuzz' test the file APIs by providing unexpected type arguments. The test
 // passes if the VM does not crash.
 
 import 'dart:async';
 import 'dart:io';
 
@@ skipping 46 matching lines @@
         futures.add(doItAsync(() => f.readAsString(encoding: v2)));
         futures.add(doItAsync(() => f.readAsLines(encoding: v2)));
       });
     });
   });
   Future.wait(futures).then((_) => asyncEnd());
 }
 
 
 fuzzSyncRandomAccessMethods() {
-  var d = new Directory('');
-  var temp = d.createTempSync();
+  var temp = Directory.systemTemp.createTempSync('dart_file_fuzz');
   var file = new File('${temp.path}/x');
   file.createSync();
   var modes = [ FileMode.READ, FileMode.WRITE, FileMode.APPEND ];
   for (var m in modes) {
     var opened = file.openSync(mode: m);
     typeMapping.forEach((k, v) {
       doItSync(() => opened.setPositionSync(v));
       doItSync(() => opened.truncateSync(v));
       doItSync(() => opened.writeByteSync(v));
     });
     for (var p in typePermutations(2)) {
       doItSync(() => opened.writeStringSync(p[0], encoding: p[1]));
     }
     for (var p in typePermutations(3)) {
       doItSync(() => opened.readIntoSync(p[0], p[1], p[2]));
       doItSync(() => opened.writeFromSync(p[0], p[1], p[2]));
     }
     opened.closeSync();
   }
   temp.deleteSync(recursive: true);
 }
 
 fuzzAsyncRandomAccessMethods() {
   var d = new Directory('');
-  var temp = d.createTempSync();
+  var temp = Directory.systemTemp.createTempSync('dart_file_fuzz');
   var file = new File('${temp.path}/x');
   file.createSync();
   var modes = [ FileMode.READ, FileMode.WRITE, FileMode.APPEND ];
   var futures = [];
   var openedFiles = [];
   for (var m in modes) {
     var opened = file.openSync(mode: m);
     openedFiles.add(opened);
     typeMapping.forEach((k, v) {
         futures.add(doItAsync(() => opened.setPosition(v)));
@@ skipping 15 matching lines @@
     temp.deleteSync(recursive: true);
   });
 }
 
 main() {
   fuzzSyncMethods();
   fuzzAsyncMethods();
   fuzzSyncRandomAccessMethods();
   fuzzAsyncRandomAccessMethods();
 }