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

sdk/lib/async/stream_controller.dart

Index: sdk/lib/async/stream_controller.dart
diff --git a/sdk/lib/async/stream_controller.dart b/sdk/lib/async/stream_controller.dart
index 50490f5976d76a45c80302557b07e96b19ef4878..fe3fbddc72973bff4d4a5d909155a5da1540c08f 100644
--- a/sdk/lib/async/stream_controller.dart
+++ b/sdk/lib/async/stream_controller.dart
@@ -415,6 +415,11 @@ abstract class _StreamController<T> implements StreamController<T>,
    */
   void addError(Object error, [StackTrace stackTrace]) {
     if (!_mayAddEvent) throw _badEventState();
+    AsyncError replacement = Zone.current.errorCallback(error, stackTrace);
+    if (replacement != null) {
+      error = replacement.error;
+      stackTrace = replacement.stackTrace;
+    }
     _addError(error, stackTrace);
   }
 
@@ -436,13 +441,17 @@ abstract class _StreamController<T> implements StreamController<T>,
       return _ensureDoneFuture();
     }
     if (!_mayAddEvent) throw _badEventState();
+    _closeUnchecked();
+    return _ensureDoneFuture();
+  }
+
+  void _closeUnchecked() {
     _state |= _STATE_CLOSED;
     if (hasListener) {
       _sendDone();
     } else if (_isInitialState) {
       _ensurePendingEvents().add(const _DelayedDone());
     }
-    return _ensureDoneFuture();
   }
 
   // EventSink interface. Used by the [addStream] events.