Add error-intercept for Completer.completeError and StreamController.addError.

sdk/lib/async/stream_impl.dart

 // Copyright (c) 2012, 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.
 
 part of dart.async;
 
 /** Abstract and private interface for a place to put events. */
 abstract class _EventSink<T> {
   void _add(T data);
   void _addError(Object error, StackTrace stackTrace);
@@ skipping 990 matching lines @@
     } else {
       assert(_state >= _STATE_EXTRA_DATA);
       switch (_state) {
         case _STATE_EXTRA_DATA:
           _state = _STATE_FOUND;
           _current = _futureOrPrefetch;
           _futureOrPrefetch = null;
           _subscription.resume();
           return new _Future<bool>.immediate(true);
         case _STATE_EXTRA_ERROR:
-          Object prefetch = _futureOrPrefetch;
+          AsyncError prefetch = _futureOrPrefetch;
           _clear();
-          return new _Future<bool>.immediateError(prefetch);
+          return new _Future<bool>.immediateError(prefetch.error,
+                                                  prefetch.stackTrace);
         case _STATE_EXTRA_DONE:
           _clear();
           return new _Future<bool>.immediate(false);
       }
     }
   }
 
   /** Clears up the internal state when the iterator ends. */
   void _clear() {
     _subscription = null;
@@ skipping 32 matching lines @@
   void _onError(Object error, [StackTrace stackTrace]) {
     if (_state == _STATE_MOVING) {
       _Future<bool> hasNext = _futureOrPrefetch;
       // We have cancelOnError: true, so the subscription is canceled.
       _clear();
       hasNext._completeError(error, stackTrace);
       return;
     }
     _subscription.pause();
     assert(_futureOrPrefetch == null);
-    _futureOrPrefetch = error;
+    _futureOrPrefetch = new AsyncError(error, stackTrace);
     _state = _STATE_EXTRA_ERROR;
   }
 
   void _onDone() {
      if (_state == _STATE_MOVING) {
       _Future<bool> hasNext = _futureOrPrefetch;
       _clear();
       hasNext._complete(false);
       return;
     }
     _subscription.pause();
     _futureOrPrefetch = null;
     _state = _STATE_EXTRA_DONE;
   }
 }