New OutputStream interface

tests/standalone/src/ProcessStderrTest.dart

 // Copyright (c) 2011, 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.
 //
 // Process test program to test process communication.
 //
 // VMOptions=
 // VMOptions=--short_socket_read
 // VMOptions=--short_socket_write
 // VMOptions=--short_socket_read --short_socket_write
@@ skipping 26 matching lines @@
         }
         received += buffer.length;
         if (received == BUFFERSIZE) {
           process.close();
         }
       }
 
       input.dataHandler = readData;
     }
 
-    bool written = output.write(data, 0, BUFFERSIZE, dataWritten);
-    if (written) {
-      dataWritten();
-    }
+    output.write(data);
+    dataWritten();
   }
 
   static void testMain() {
     testExit();
   }
 }
 
 main() {
   ProcessStderrTest.testMain();
 }