Make IOSink implement StringSink

tests/standalone/io/file_fuzz_test.dart

-// Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
+// 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';
 import 'dart:isolate';
 
 import 'fuzz_support.dart';
 
 fuzzSyncMethods() {
   typeMapping.forEach((k, v) {
     doItSync(() {
       var f = new File(v);
       doItSync(f.existsSync);
       doItSync(f.createSync);
       doItSync(f.deleteSync);
       doItSync(f.directorySync);
       doItSync(f.lengthSync);
       doItSync(f.modifiedSync);
       doItSync(f.fullPathSync);
       doItSync(() => f.openRead().listen(() {}, onError: (e) {}));
       doItSync(f.readAsBytesSync);
       doItSync(f.readAsStringSync);
       doItSync(f.readAsLinesSync);
       typeMapping.forEach((k2, v2) {
         doItSync(() => f.openSync(v2));
-        doItSync(() => f.openWrite(v2));
+        doItSync(() => f.openWrite(mode: v2));
         doItSync(() => f.readAsStringSync(v2));
         doItSync(() => f.readAsLinesSync(v2));
       });
     });
   });
 }
 
 fuzzAsyncMethods() {
   var port = new ReceivePort();
   var futures = [];
@@ skipping 77 matching lines @@
     temp.deleteSync(recursive: true);
   });
 }
 
 main() {
   fuzzSyncMethods();
   fuzzAsyncMethods();
   fuzzSyncRandomAccessMethods();
   fuzzAsyncRandomAccessMethods();
 }