Make synchronous broadcast StreamController throw if adding event while adding event.

tests/lib/async/stream_controller_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_test;
 
 import "package:expect/expect.dart";
 import "package:async_helper/async_helper.dart";
 import 'dart:async';
@@ skipping 655 matching lines @@
   }
   int i = 1;
   c = new StreamController.broadcast(onListen: send, sync: true);
   c.stream.listen((v) {
     Expect.equals(i++, v);
   }, onDone: asyncEnd);
   c.add(2);
   c.close();
 }
 
+void testSyncControllerNotReentrant() {
+  Stream emptyStream = (new StreamController.broadcast()..close()).stream;
+  asyncStart();
+  for (int listenerCount = 1; listenerCount <= 2; listenerCount++) {
+    StreamController c = new StreamController.broadcast(sync: true);
+    for (int i = 0; i < listenerCount; i++) {
+      asyncStart();
+      asyncStart();
+      c.stream.listen((v) {
+        Expect.equals(42, v);
+        Expect.throws(() {
+          c.add(37);
+        });
+        Expect.throws(() {
+          c.addError(37);
+        });
+        Expect.throws(() {
+          c.addStream(emptyStream);
+        });
+        Expect.throws(() {
+          c.close();
+        });
+        asyncEnd();
+      }, onError: (e, s) {
+        Expect.equals(87, e);
+        Expect.throws(() {
+          c.add(37);
+        });
+        Expect.throws(() {
+          c.addError(37);
+        });
+        Expect.throws(() {
+          c.addStream(emptyStream);
+        });
+        Expect.throws(() {
+          c.close();
+        });
+        asyncEnd();
+      });
+    }
+    c.add(42);
+    c.addError(87);
+  }
+  asyncEnd();
+}
+
 main() {
   asyncStart();
   testMultiController();
   testSingleController();
   testExtraMethods();
   testClosed();
   testCloseFuture();
   testCloseFuture2();
   testCloseFuture3();
   testStreamEquals();
   testCancelThrow();
   testCancelThrow2();
   testCancelThrow3();
   testBroadcastListenAfterClose();
   testBroadcastListenAfterClosePaused();
   testAsBroadcastListenAfterClose();
   testAsBroadcastListenAfterClosePaused();
   testEventInListen();
+  testSyncControllerNotReentrant();
   asyncEnd();
 }