Let StreamSubscription.cancel return a Future.

tests/lib/async/stream_controller_async_test.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.
 
 // Test the basic StreamController and StreamController.singleSubscription.
 library stream_controller_async_test;
 
 import 'dart:async';
 import 'dart:isolate';
 import "package:expect/expect.dart";
@@ skipping 261 matching lines @@
 
     StreamProtocolTest test = new StreamProtocolTest();
     Completer completer = new Completer();
     test..expectListen()
         ..expectData(42, () { test.pause(completer.future); })
         ..expectPause(() {
             completer.complete(null);
           })
         ..expectData(43)
         ..expectData(44)
-        ..expectDone()
-        ..expectCancel(test.terminate);
+        ..expectCancel()
+        ..expectDone(test.terminate);
     test.listen();
     test.add(42);
     test.add(43);
     test.add(44);
     test.close();
   });
 
   test("pause twice event-unpause", () {
     StreamProtocolTest test = new StreamProtocolTest();
     Completer completer = new Completer();
     Completer completer2 = new Completer();
     test..expectListen()
         ..expectData(42, () {
             test.pause(completer.future);
             test.pause(completer2.future);
           })
         ..expectPause(() {
             completer.future.then(completer2.complete);
             completer.complete(null);
           })
         ..expectData(43)
         ..expectData(44)
-        ..expectDone()
-        ..expectCancel(test.terminate);
+        ..expectCancel()
+        ..expectDone(test.terminate);
     test..listen()
         ..add(42)
         ..add(43)
         ..add(44)
         ..close();
   });
 
   test("pause twice direct-unpause", () {
     StreamProtocolTest test = new StreamProtocolTest();
     test..expectListen()
         ..expectData(42, () {
             test.pause();
             test.pause();
           })
         ..expectPause(() {
             test.resume();
             test.resume();
           })
         ..expectData(43)
         ..expectData(44)
-        ..expectDone()
-        ..expectCancel(test.terminate);
+        ..expectCancel()
+        ..expectDone(test.terminate);
     test..listen()
         ..add(42)
         ..add(43)
         ..add(44)
         ..close();
   });
 
   test("pause twice direct-event-unpause", () {
     StreamProtocolTest test = new StreamProtocolTest();
     Completer completer = new Completer();
     test..expectListen()
         ..expectData(42, () {
             test.pause();
             test.pause(completer.future);
             test.add(43);
             test.add(44);
             test.close();
           })
         ..expectPause(() {
             completer.future.then((v) => test.resume());
             completer.complete(null);
           })
         ..expectData(43)
         ..expectData(44)
-        ..expectDone()
-        ..expectCancel(test.terminate);
+        ..expectCancel()
+        ..expectDone(test.terminate);
     test..listen()
         ..add(42);
   });
 }
 
 class TestError { const TestError(); }
 
 testRethrow() {
   TestError error = const TestError();
 
@@ skipping 44 matching lines @@
   testFuture("reduce", (s, act) => s.reduce((a,b) => act(b)));
   testFuture("fold", (s, act) => s.fold(0, (a,b) => act(b)));
   testFuture("drain", (s, act) => s.drain().then(act));
 }
 
 void testBroadcastController() {
   test("broadcast-controller-basic", () {
     StreamProtocolTest test = new StreamProtocolTest.broadcast();
     test..expectListen()
         ..expectData(42)
-        ..expectDone()
-        ..expectCancel(test.terminate);
+        ..expectCancel()
+        ..expectDone(test.terminate);
     test..listen()
         ..add(42)
         ..close();
   });
 
   test("broadcast-controller-listen-twice", () {
     StreamProtocolTest test = new StreamProtocolTest.broadcast();
     test..expectListen()
         ..expectData(42, () {
             test.listen();
             test.add(37);
             test.close();
           })
       // Order is not guaranteed between subscriptions if not sync.
         ..expectData(37)
         ..expectData(37)
         ..expectDone()
-        ..expectDone()
-        ..expectCancel(test.terminate);
+        ..expectCancel()
+        ..expectDone(test.terminate);
     test.listen();
     test.add(42);
   });
 
   test("broadcast-controller-listen-twice-non-overlap", () {
     StreamProtocolTest test = new StreamProtocolTest.broadcast();
     test
     ..expectListen(() {
       test.add(42);
     })
     ..expectData(42, () {
       test.cancel();
     })
     ..expectCancel(() {
       test.listen();
     })..expectListen(() {
       test.add(37);
     })
     ..expectData(37, () {
       test.close();
     })
-    ..expectDone()
-    ..expectCancel(test.terminate);
+    ..expectCancel()
+    ..expectDone(test.terminate);
     test.listen();
   });
 
   test("broadcast-controller-individual-pause", () {
     StreamProtocolTest test = new StreamProtocolTest.broadcast();
     var sub1;
     test..expectListen()
         ..expectData(42)
         ..expectData(42, () { sub1.pause(); })
         ..expectData(43, () {
@@ skipping 79 matching lines @@
         ..expectPause(() {
             sub = test.listen();
           })
         ..expectBroadcastListen((originalSub) {
             originalSub.resume();
           })
         ..expectData(43)
         ..expectResume(() {
             test.close();
           })
+        ..expectCancel()
         ..expectDone()
-        ..expectBroadcastCancel()
-        ..expectCancel(test.terminate);
+        ..expectBroadcastCancel((_) => test.terminate());
     sub = test.listen();
   });
 }
 
 void testSink({bool sync, bool broadcast, bool asBroadcast}) {
   String type = "${sync?"S":"A"}${broadcast?"B":"S"}${asBroadcast?"aB":""}";
   test("$type-controller-sink", () {
     var done = expectAsync0((){});
     var c = broadcast ? new StreamController.broadcast(sync: sync)
                       : new StreamController(sync: sync);
@@ skipping 109 matching lines @@
   testRethrow();
   testBroadcastController();
   testAsBroadcast();
   testSink(sync: true, broadcast: false, asBroadcast: false);
   testSink(sync: true, broadcast: false, asBroadcast: true);
   testSink(sync: true, broadcast: true, asBroadcast: false);
   testSink(sync: false, broadcast: false, asBroadcast: false);
   testSink(sync: false, broadcast: false, asBroadcast: true);
   testSink(sync: false, broadcast: true, asBroadcast: false);
 }