Fix test to make sure that all opened file descriptors for a File

tests/standalone/src/io/FileTest.dart

 // Copyright (c) 2012, 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.
 //
 // Dart test program for testing file I/O.
 
 #import("dart:io");
 #import("dart:isolate");
 
 class MyListOfOneElement implements List {
@@ skipping 292 matching lines @@
   static void testOutputStreamWriteAppend() {
     String content = "foobar";
     String filename = tempDirectory.path + "/outstream_write_append";
     File file = new File(filename);
     file.createSync();
     List<int> buffer = content.charCodes();
     OutputStream outStream = file.openOutputStream();
     outStream.write(buffer);
     outStream.onNoPendingWrites = () {
       outStream.close();
-      File file2 = new File(filename);
-      OutputStream appendingOutput =
-          file2.openOutputStream(FileMode.APPEND);
-      appendingOutput.write(buffer);
-      appendingOutput.onNoPendingWrites = () {
-        appendingOutput.close();
-        File file3 = new File(filename);
-        file3.open(FileMode.READ, (RandomAccessFile openedFile) {
-          openedFile.length((int length) {
-            Expect.equals(content.length * 2, length);
-            openedFile.close(() {
-              file3.delete(() {
-                asyncTestDone("testOutputStreamWriteAppend");
+      outStream.onClosed = () {
+        File file2 = new File(filename);
+        OutputStream appendingOutput =
+            file2.openOutputStream(FileMode.APPEND);
+        appendingOutput.write(buffer);
+        appendingOutput.onNoPendingWrites = () {
+          appendingOutput.close();
+          appendingOutput.onClosed = () {
+            File file3 = new File(filename);
+            file3.open(FileMode.READ, (RandomAccessFile openedFile) {
+              openedFile.length((int length) {
+                Expect.equals(content.length * 2, length);
+                openedFile.close(() {
+                  file3.delete(() {
+                    asyncTestDone("testOutputStreamWriteAppend");
+                  });
+                });
               });
             });
-          });
-        });
+          };
+        };
       };
     };
     asyncTestStarted();
   }
 
   // Test for file read and write functionality.
   static void testOutputStreamWriteString() {
     String content = "foobar";
     String filename = tempDirectory.path + "/outstream_write_string";
     File file = new File(filename);
@@ skipping 739 matching lines @@
       testWriteVariousLists();
       testDirectory();
       testDirectorySync();
     });
   }
 }
 
 main() {
   FileTest.testMain();
 }