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

tests/lib/async/catch_errors24_test.dart

Index: tests/lib/async/catch_errors24_test.dart
diff --git a/tests/lib/async/catch_errors24_test.dart b/tests/lib/async/catch_errors24_test.dart
index 127f18e0e63c6f1a75dbe5fe14ca0a9763a6fd94..309611aa39c1a82440782f271b5136d88cc665ef 100644
--- a/tests/lib/async/catch_errors24_test.dart
+++ b/tests/lib/async/catch_errors24_test.dart
@@ -20,6 +20,8 @@ main() {
   catchErrors(() {
     catchErrors(() {
       controller = new StreamController();
+
+      // Assign to the "global" `stream`.
       stream = controller.stream
         .map((x) {
           events.add("map $x");
@@ -28,6 +30,8 @@ main() {
         .transform(new StreamTransformer.fromHandlers(
             handleError: (e, st, sink) { sink.add("error $e"); }))
         .asBroadcastStream();
+
+      // Listen to the `stream` in the inner zone (but wait in a microtask).
       scheduleMicrotask(() {
         stream.listen((x) {
           events.add("stream $x");
@@ -36,12 +40,13 @@ main() {
       });
     }).listen((x) { events.add(x); })
       .asFuture().then((_) { Expect.fail("Unexpected callback"); });
+
+    // Listen to `stream` from the outer zone.
     stream.listen((x) { events.add("stream2 $x"); });
+
+    // Feed the controller, but wait in a microtask.
     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();
     });
@@ -52,10 +57,10 @@ main() {
     // Give handlers time to complete.
     Timer.run(() {
       Expect.listEquals(["map 1",
-                          "stream2 101",
-                          "stream 101",
-                          "stream2 error 2",
-                          "stream error 2",
+                         "stream2 101",
+                         "stream 101",
+                         "stream2 error 2",
+                         "stream error 2",
                         ],
                         events);
       asyncEnd();