Redo StreamTransformers so they work with Stack traces.

tests/lib/async/stream_transformer_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 'package:async_helper/async_helper.dart';
+import 'dart:async';
+import 'event_helper.dart';
+
+_defaultData(x) {}
+_defaultError(e, [st]) {}
+_defaultDone() {}
+
+/// Dummy StreamSubscription.
+class MyStreamSubscription<T> implements StreamSubscription<T> {
+  final Stream stream;
+  final bool cancelOnError;
+  Function handleData = null;
+  Function handleError = null;
+  Function handleDone = null;
+
+  MyStreamSubscription(this.stream, this.cancelOnError);
+
+  void cancel() {}
+  void onData(void handleData(T data)) {
+    this.handleData = handleData == null ? _defaultData: handleData;
+  }
+  void onError(Function handleError) {
+    this.handleError = handleError == null ? _defaultError: handleError;
+  }
+  void onDone(void handleDone()) {
+    this.handleDone = handleDone == null ? _defaultDone: handleDone;
+  }
+
+  void pause([Future resumeSignal]) {}
+  final isPaused = false;
+  Future asFuture([var futureValue]) => null;
+}
+
+main() {
+  var transformer = new StreamTransformer<int, String> (
+    (stream, cancelOnError) => new MyStreamSubscription(stream, cancelOnError));
+
+  var controller = new StreamController(sync: true);
+  var stream = controller.stream;
+  var transformed = stream.transform(transformer);
+
+  var handleData = (String _) => 499;
+  var handleError = (e,st) => 42;
+  var handleDone = () => 99;
+
+  var subscription =
+      transformed.listen(handleData, onError: handleError, onDone: handleDone);
+
+  Expect.identical(stream, subscription.stream);
+  Expect.equals(false, subscription.cancelOnError);
+  Expect.identical(handleData, subscription.handleData);
+  Expect.identical(handleError, subscription.handleError);
+  Expect.identical(handleDone, subscription.handleDone);
+
+  // Note that we reuse the transformer.
+
+  controller = new StreamController(sync: true);
+  stream = controller.stream;
+  transformed = stream.transform(transformer);
+  subscription = transformed.listen(null);
+
+  Expect.identical(stream, subscription.stream);
+  Expect.equals(false, subscription.cancelOnError);
+  Expect.identical(_defaultData, subscription.handleData);
+  Expect.identical(_defaultError, subscription.handleError);
+  Expect.identical(_defaultDone, subscription.handleDone);
+
+  controller = new StreamController(sync: true);
+  stream = controller.stream;
+  transformed = stream.transform(transformer);
+  subscription =
+      transformed.listen(null, onDone: handleDone, cancelOnError: true);
+
+  Expect.identical(stream, subscription.stream);
+  Expect.equals(true, subscription.cancelOnError);
+  Expect.identical(_defaultData, subscription.handleData);
+  Expect.identical(_defaultError, subscription.handleError);
+  Expect.identical(handleDone, subscription.handleDone);
+}