Rename unsubscribe to cancel.

tests/lib/async/slow_consumer_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.
 
 // VMOptions=--old_gen_heap_size=32
 
 import 'dart:async';
 import 'dart:isolate';
 
 const int KB = 1024;
 const int MB = KB * KB;
 const int GB = KB * KB * KB;
 
 class SlowConsumer extends StreamPipe {
   var current = new Future.immediate(0);
   final int bytesPerSecond;
 
   SlowConsumer(int this.bytesPerSecond);
 
   Future bind(Stream stream) {
     Completer completer = new Completer();
     var subscription;
-    subscription = stream.subscribe(
-      onData: (List<int> data) {
+    subscription = stream.listen(
+      (List<int> data) {
         current = current
           .then((count) {
             // Simulated amount of time it takes to handle the data.
             int ms = data.length * 1000 ~/ bytesPerSecond;
             subscription.pause();
             return new Future.delayed(ms, () {
               subscription.resume();
               // Make sure we use data here to keep tracking it.
               return count + data.length;
             });
@@ skipping 48 matching lines @@
   // file). If the consumer doesn't pause the data-provider it will run out of
   // heap-space.
 
   new DataProvider(800 * MB, 100 * MB, 1 * MB)
     .pipe(new SlowConsumer(200 * MB))
     .then((count) {
       port.close();
       Expect.equals(100 * MB, count);
     });
 }