Gracefully handle tests that print.

lib/src/backend/invoker.dart

 // Copyright (c) 2015, 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.
 
 library unittest.backend.invoker;
 
 import 'dart:async';
 
 import 'package:stack_trace/stack_trace.dart';
 
@@ skipping 160 matching lines @@
           return new Future.sync(_test._tearDown);
         }).catchError(Zone.current.handleUncaughtError).then((_) {
           timer.cancel();
           _controller.setState(
               new State(Status.complete, liveTest.state.result));
 
           // Use [Timer.run] here to avoid starving the DOM or other
           // non-microtask events.
           Timer.run(_controller.completer.complete);
         });
-      }, zoneValues: {#unittest.invoker: this}, onError: handleError);
+      },
+          zoneSpecification: new ZoneSpecification(
+              print: (self, parent, zone, line) => _controller.print(line)),
+          zoneValues: {#unittest.invoker: this},
+          onError: handleError);
     });
   }
 }