catchErrors and waitForCompletion now based on runZonedExperimental.

tests/lib/async/catch_errors.dart

+library catch_errors;
+
+import 'dart:async';
+
+Stream catchErrors(void body()) {
+  StreamController controller;
+
+  bool onError(e) {
+    controller.add(e);
+    return true;
+  }
+
+  void onDone() {
+    controller.close();
+  }
+
+  void onListen() {
+    runZonedExperimental(body, onError: onError, onDone: onDone);
+  }
+
+  controller = new StreamController(onListen: onListen);
+  return controller.stream;
+}
+
+Future waitForCompletion(void body()) {
+  Completer completer = new Completer.sync();
+  runZonedExperimental(body, onDone: completer.complete);
+  return completer.future;
+}