Add a ListOutputStream.onData callback.

tests/standalone/io/list_input_stream_test.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.
 
 #import("dart:io");
 #import("dart:isolate");
 
 void testEmptyListInputStream() {
   ListInputStream stream = new ListInputStream();
   stream.write([]);
@@ skipping 87 matching lines @@
 
 void testListInputStreamPipe1() {
   List<int> data = [0x00, 0x01, 0x10, 0x11, 0x7e, 0x7f, 0x80, 0x81, 0xfe, 0xff];
   ListInputStream input = new ListInputStream();
   input.write(data);
   input.markEndOfStream();
   ListOutputStream output = new ListOutputStream();
   ReceivePort donePort = new ReceivePort();
 
   void onClosed() {
-    var contents = output.contents();
+    var contents = output.read();
     Expect.equals(data.length, contents.length);
     donePort.toSendPort().send(null);
   }
 
   input.onClosed = onClosed;
   input.pipe(output);
 
   donePort.receive((x,y) => donePort.close());
 }
 
 void testListInputStreamPipe2() {
   List<int> data = [0x00, 0x01, 0x10, 0x11, 0x7e, 0x7f, 0x80, 0x81, 0xfe, 0xff];
   ListOutputStream output = new ListOutputStream();
   ReceivePort donePort = new ReceivePort();
   int count = 0;
 
   void onClosed() {
     if (count < 10) {
       ListInputStream input = new ListInputStream();
       input.write(data);
       input.markEndOfStream();
       input.onClosed = onClosed;
       if (count < 9) {
         input.pipe(output, close: false);
       } else {
         input.pipe(output);
       }
       count++;
     } else {
-      var contents = output.contents();
+      var contents = output.read();
       Expect.equals(data.length * 10, contents.length);
       donePort.toSendPort().send(null);
     }
   }
 
   ListInputStream input = new ListInputStream();
   input.write(data);
   input.markEndOfStream();
   input.onClosed = onClosed;
   input.pipe(output, close: false);
@@ skipping 133 matching lines @@
   testListInputStream1();
   testListInputStream2();
   testListInputStreamPipe1();
   testListInputStreamPipe2();
   testListInputClose1();
   testListInputClose2();
   testDynamicListInputStream();
   testDynamicListInputClose1();
   testDynamicListInputClose2();
 }