catchErrors and waitForCompletion now based on runZonedExperimental.

tests/lib/async/run_zoned6_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:expect/expect.dart";
+import 'dart:async';
+import 'dart:isolate';
+
+main() {
+  // We keep a ReceivePort open until all tests are done. This way the VM will
+  // hang if the callbacks are not invoked and the test will time out.
+  var port = new ReceivePort();
+  // Ensure that `runZoned`'s onError handles synchronous errors but delegates
+  // to the top-level when the handler returns false.
+  try {
+    runZonedExperimental(() { throw 0; },
+                        onError: (e) {
+                          Expect.equals(0, e);
+                          port.close();
+                          return false;  /// 01: runtime error
+                          return true;
+                        });
+  } catch (e) {
+    // We should never see an error here.
+    if (true)  /// 01: continued
+      rethrow;
+  }
+}