Return futures on Stream.cancel when possible.

tests/lib/async/stream_subscription_as_future_test.dart

 // Copyright (c) 2013, 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.
 
 // Test the Stream.single method.
 library stream_single_test;
 
 import "package:expect/expect.dart";
 import 'dart:async';
 import 'package:unittest/unittest.dart';
 
 main() {
-  test("subscription.asStream success", () {
+  test("subscription.asFuture success", () {
     Stream stream = new Stream.fromIterable([1, 2, 3]);
     var output = [];
     var subscription = stream.listen((x) { output.add(x); });
     subscription.asFuture(output).then(expectAsync((o) {
       Expect.listEquals([1, 2, 3], o);
     }));
   });
 
-  test("subscription.asStream success2", () {
+  test("subscription.asFuture success2", () {
     StreamController controller = new StreamController(sync: true);
     [1, 2, 3].forEach(controller.add);
     controller.close();
     Stream stream = controller.stream;
     var output = [];
     var subscription = stream.listen((x) { output.add(x); });
     subscription.asFuture(output).then(expectAsync((o) {
       Expect.listEquals([1, 2, 3], o);
     }));
   });
 
-  test("subscription.asStream success 3", () {
+  test("subscription.asFuture success 3", () {
     Stream stream = new Stream.fromIterable([1, 2, 3]).map((x) => x);
     var output = [];
     var subscription = stream.listen((x) { output.add(x); });
     subscription.asFuture(output).then(expectAsync((o) {
       Expect.listEquals([1, 2, 3], o);
     }));
   });
 
-  test("subscription.asStream different type", () {
+  test("subscription.asFuture different type", () {
     Stream stream = new Stream<int>.fromIterable([1, 2, 3]);
     var asyncCallback = expectAsync(() => {});
     var output = [];
     var subscription = stream.listen((x) { output.add(x); });
     subscription.asFuture("string").then((String o) {
       Expect.listEquals([1, 2, 3], output);
       Expect.equals("string", o);
       asyncCallback();
     });
   });
 
-  test("subscription.asStream failure", () {
+  test("subscription.asFuture failure", () {
     StreamController controller = new StreamController(sync: true);
     [1, 2, 3].forEach(controller.add);
     controller.addError("foo");
     controller.close();
     Stream stream = controller.stream;
     var output = [];
     var subscription = stream.listen((x) { output.add(x); });
     subscription.asFuture(output).catchError(expectAsync((error) {
       Expect.equals(error, "foo");
     }));
   });
 
-  test("subscription.asStream failure2", () {
+  test("subscription.asFuture failure2", () {
     Stream stream = new Stream.fromIterable([1, 2, 3, 4])
       .map((x) {
         if (x == 4) throw "foo";
         return x;
       });
     var output = [];
     var subscription = stream.listen((x) { output.add(x); });
     subscription.asFuture(output).catchError(expectAsync((error) {
       Expect.equals(error, "foo");
     }));
   });
+
+  test("subscription.asFuture delayed cancel", () {
+    var completer = new Completer();
+    var controller =
+        new StreamController(onCancel: () => completer.future, sync: true);
+    [1, 2, 3].forEach(controller.add);
+    controller.addError("foo");
+    controller.close();
+    Stream stream = controller.stream;
+    var output = [];
+    var subscription = stream.listen((x) { output.add(x); });
+    bool catchErrorHasRun = false;
+    subscription.asFuture(output).catchError(expectAsync((error) {
+      Expect.equals(error, "foo");
+      catchErrorHasRun = true;
+    }));
+    Timer.run(expectAsync(() {
+      Expect.isFalse(catchErrorHasRun);
+      completer.complete();
+    }));
+  });
 }