Redo StreamTransformers so they work with Stack traces.

tests/lib/async/stream_event_transform_test.dart

-// Copyright (c) 2011, 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 stream_event_transform_test;
-
-import "package:expect/expect.dart";
-import 'dart:async';
-import '../../../pkg/unittest/lib/unittest.dart';
-import 'event_helper.dart';
-
-void handleData(int data, EventSink<int> sink) {
-  sink.addError("$data");
-  sink.add(data + 1);
-}
-
-void handleError(error, EventSink<int> sink) {
-  String value = error;
-  int data = int.parse(value);
-  sink.add(data);
-  sink.addError("${data + 1}");
-}
-
-void handleDone(EventSink<int> sink) {
-  sink.add(99);
-  sink.close();
-}
-
-class EventTransformer extends StreamEventTransformer<int,int> {
-  void handleData(int data, EventSink<int> sink) {
-    sink.addError("$data");
-    sink.add(data + 1);
-  }
-
-  void handleError(String value, EventSink<int> sink) {
-    int data = int.parse(value);
-    sink.add(data);
-    sink.addError("${data + 1}");
-  }
-
-  void handleDone(EventSink<int> sink) {
-    sink.add(99);
-    sink.close();
-  }
-}
-
-main() {
-  {
-    StreamController c = new StreamController(sync: true);
-    Events expected = new Events()..error("0")..add(1)
-                                  ..error("1")..add(2)
-                                  ..add(3)..error("4")
-                                  ..add(99)..close();
-    Events input = new Events()..add(0)..add(1)..error("3")..close();
-    Events actual = new Events.capture(
-        c.stream.transform(new EventTransformer()));
-    actual.onDone(() {
-      Expect.listEquals(expected.events, actual.events);
-    });
-    input.replay(c);
-  }
-
-  {
-    StreamController c = new StreamController(sync: true);
-    Events expected = new Events()..error("0")..add(1)
-                                  ..error("1")..add(2)
-                                  ..add(3)..error("4")
-                                  ..add(99)..close();
-    Events input = new Events()..add(0)..add(1)..error("3")..close();
-    Events actual = new Events.capture(
-        c.stream.transform(new StreamTransformer(
-            handleData: handleData,
-            handleError: handleError,
-            handleDone: handleDone
-        )));
-    actual.onDone(() {
-      Expect.listEquals(expected.events, actual.events);
-    });
-    input.replay(c);
-  }
-}