Make Zone API strong mode clean.

sdk/lib/async/stream_impl.dart

Index: sdk/lib/async/stream_impl.dart
diff --git a/sdk/lib/async/stream_impl.dart b/sdk/lib/async/stream_impl.dart
index b5e89c17f52d5d653ba8f28fe85e8b4423f74052..1ce2acf6846332e2d5617df94cc6bb7e3876ecb2 100644
--- a/sdk/lib/async/stream_impl.dart
+++ b/sdk/lib/async/stream_impl.dart
@@ -332,7 +332,7 @@ class _BufferingStreamSubscription<T>
     _checkState(wasInputPaused);
   }
 
-  void _sendError(var error, StackTrace stackTrace) {
+  void _sendError(Object error, StackTrace stackTrace) {
     assert(!_isCanceled);
     assert(!_isPaused);
     assert(!_inCallback);
@@ -345,12 +345,11 @@ class _BufferingStreamSubscription<T>
       _state |= _STATE_IN_CALLBACK;
       // TODO(floitsch): this dynamic should be 'void'.
       if (_onError is ZoneBinaryCallback<dynamic, Object, StackTrace>) {
-        ZoneBinaryCallback<dynamic, Object, StackTrace> errorCallback = _onError
-            as Object/*=ZoneBinaryCallback<dynamic, Object, StackTrace>*/;
+        ZoneBinaryCallback<dynamic, Object, StackTrace> errorCallback =
+            _onError;
         _zone.runBinaryGuarded(errorCallback, error, stackTrace);
       } else {
-        _zone.runUnaryGuarded<dynamic, Object>(
-            _onError as Object/*=ZoneUnaryCallback<dynamic, Object>*/, error);
+        _zone.runUnaryGuarded<Object>(_onError, error);
       }
       _state &= ~_STATE_IN_CALLBACK;
     }