Loosen type check on runZoned errorHandler

sdk/lib/async/zone.dart

Index: sdk/lib/async/zone.dart
diff --git a/sdk/lib/async/zone.dart b/sdk/lib/async/zone.dart
index 33cc592a4581ee22a2ae0d8182b1837eba3d82fa..573603627f24ad056ffbb04ce72c4feeaded51d2 100644
--- a/sdk/lib/async/zone.dart
+++ b/sdk/lib/async/zone.dart
@@ -1438,7 +1438,8 @@ R runZoned<R>(R body(),
     errorHandler = (Zone self, ZoneDelegate parent, Zone zone, error,
         StackTrace stackTrace) {
       try {
-        if (onError is ZoneBinaryCallback<R, Object, StackTrace>) {
+        // TODO(floitsch): the return type should be 'void'.
+        if (onError is ZoneBinaryCallback<dynamic, Object, StackTrace>) {
           return self.parent.runBinary(onError, error, stackTrace);
         }
         return self.parent.runUnary(onError, error);