Do not compare the output before we know it has all been written.

tests/standalone/src/StreamPipeTest.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.
 //
 // VMOptions=
 // VMOptions=--short_socket_read
 // VMOptions=--short_socket_write
 // VMOptions=--short_socket_read --short_socket_write
 
 #library("StreamPipeTest");
@@ skipping 78 matching lines @@
         var tempDir = new Directory('');
         tempDir.createTempSync();
         var dstFileName = tempDir.path + "/readline_test1.dat";
         var dstFile = new File(dstFileName);
         dstFile.createSync();
         var fileOutput = dstFile.openOutputStream();
 
         socketInput.closeHandler = () {
           // Check that the resulting file is equal to the initial
           // file.
-          bool result = compareFileContent(srcFileName, dstFileName);
           fileOutput.closeHandler = () {
+            bool result = compareFileContent(srcFileName, dstFileName);
             new File(dstFileName).deleteSync();
             tempDir.deleteSync();
             Expect.isTrue(result);
 
             _socket.close();
 
             // Run this twice.
             if (count++ < 2) {
               runTest();
             } else {
@@ skipping 175 matching lines @@
   srcStream.pipe(dstStream, close: false);
 }
 
 
 main() {
   testFileToFilePipe1();
   testFileToFilePipe2();
   testFileToFilePipe3();
   PipeServerGame echoServerGame = new PipeServerGame.start();
 }