Don't consider controller.addError to be a zone-crossing.

tests/lib/async/catch_errors27_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.
 
 import 'package:async_helper/async_helper.dart';
 import "package:expect/expect.dart";
 import 'dart:async';
 import 'catch_errors.dart';
 
 main() {
   asyncStart();
   Completer done = new Completer();
 
   var events = [];
   StreamController controller;
   Stream stream;
-  // Test that the first listen on a `asBroadcastStream` determines the
-  // zone the subscription lives in. The inner listen happens first, and
-  // the outer listener must not see the error since it would cross a
-  // zone boundary. It is therefore given to the inner `catchErrors`.
+  // Test that streams live in the zone they have been listened too.
+  // It doesn't matter how many zone-boundaries the stream traverses. What
+  // counts is the zone where `listen` was invoked.
   catchErrors(() {
     catchErrors(() {
       controller = new StreamController();
+
+      // Assignment to "global" `stream`.
       stream = controller.stream
         .map((x) {
           events.add("map $x");
           return x + 100;
         })
         .asBroadcastStream();
+
+      // Consume stream in the nested zone.
       stream
         .transform(new StreamTransformer.fromHandlers(
             handleError: (e, st, sink) { sink.add("error $e"); }))
         .listen((x) { events.add("stream $x"); });
+
+      // Feed the controller in the nested zone.
       scheduleMicrotask(() {
         controller.add(1);
-        // Errors are not allowed to traverse boundaries, but in this case the
-        // first listener of the broadcast stream is in the same error-zone. So
-        // this should work.
         controller.addError(2);
         controller.close();
+        new Future.error("done");
       });
+
     }).listen((x) {
-                events.add(x);
-                if (x == 2) done.complete(true);
+                events.add("listen: $x");
+                if (x == "done") done.complete(true);
               })
       .asFuture().then((_) { Expect.fail("Unexpected callback"); });
+
+    // Listen to stream in outer zone.
     stream.listen((x) { events.add("stream2 $x"); });
   }).listen((x) { events.add("outer: $x"); },
             onDone: () { Expect.fail("Unexpected callback"); });
 
   done.future.whenComplete(() {
     // Give handlers time to run.
     Timer.run(() {
       Expect.listEquals(["map 1",
-                          "stream 101",
-                          "stream2 101",
-                          "stream error 2",
-                          2, // Caught by the inner `catchErrors`.
+                         "stream 101",
+                         "stream2 101",
+                         "stream error 2",
+                         "listen: done",
+                         "outer: 2",
                         ],
                         events);
       asyncEnd();
     });
   });
 }