Add an [immediate] argument to StreamQueue.cancel.

test/stream_queue_test.dart

Index: test/stream_queue_test.dart
diff --git a/test/stream_queue_test.dart b/test/stream_queue_test.dart
index e5fe25cf4687e33119d29f26512c2d010732bddc..cad0ad511669f3f29ca9f44e4e639b31f57a35bd 100644
--- a/test/stream_queue_test.dart
+++ b/test/stream_queue_test.dart
@@ -333,7 +333,7 @@ main() {
     });
   });
 
-  group("close operation", () {
+  group("cancel operation", () {
     test("closes the events, prevents any other operation", () async {
       var events = new StreamQueue<int>(createStream());
       await events.cancel();
@@ -352,8 +352,62 @@ main() {
       expect(await events.next, 1);
       expect(await events.cancel(), 42);
     });
-  });
 
+    group("with immediate: true", () async {
+      test("closes the events, prevents any other operation", () async {
+        var events = new StreamQueue<int>(createStream());
+        await events.cancel(immediate: true);
+        expect(() => events.next, throwsStateError);
+        expect(() => events.skip(1), throwsStateError);
+        expect(() => events.take(1), throwsStateError);
+        expect(() => events.rest, throwsStateError);
+        expect(() => events.cancel(), throwsStateError);
+      });
+
+      test("cancels the underlying subscription immediately", () async {
+        var controller = new StreamController();
+        controller.add(1);
+
+        var events = new StreamQueue<int>(controller.stream);
+        expect(await events.next, 1);
+        expect(controller.hasListener, isTrue);
+
+        events.cancel(immediate: true);
+        await expect(controller.hasListener, isFalse);
+      });
+
+      test("closes pending requests", () async {
+        var events = new StreamQueue<int>(createStream());
+        expect(await events.next, 1);
+        expect(events.next, throwsStateError);
+        expect(events.hasNext, completion(isFalse));
+
+        await events.cancel(immediate: true);
+      });
+
+      test("returns the result of closing the underlying subscription",
+          () async {
+        var controller = new StreamController(
+            onCancel: () => new Future.value(42));
+        var events = new StreamQueue<int>(controller.stream);
+        expect(await events.cancel(immediate: true), 42);
+      });
+
+      test("listens and then cancels a stream that hasn't been listened to yet",
+          () async {
+        var wasListened = false;
+        var controller = new StreamController(
+            onListen: () => wasListened = true);
+        var events = new StreamQueue<int>(controller.stream);
+        expect(wasListened, isFalse);
+        expect(controller.hasListener, isFalse);
+
+        await events.cancel(immediate: true);
+        expect(wasListened, isTrue);
+        expect(controller.hasListener, isFalse);
+      });
+    });
+  });
 
   group("hasNext operation", () {
     test("true at start", () async {