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 1d4e12247e1de14aad9b8b62ff0b7d89716c0f93..09cc1151b20a673d0752d8390bd66247337da3c1 100644
--- a/sdk/lib/async/zone.dart
+++ b/sdk/lib/async/zone.dart
@@ -1438,7 +1438,7 @@ R runZoned<R>(R body(),
     errorHandler = (Zone self, ZoneDelegate parent, Zone zone, error,
         StackTrace stackTrace) {
       try {
-        if (onError is ZoneBinaryCallback<R, Object, StackTrace>) {

[vsm, 2017/05/03 01:35:48]

We're failing this is-check now when onError is a (Object, [StackTrace]) =>
Void.  That's causing us to fall into the runUnary path and report suboptimal
errors on internal tests.

[Lasse Reichstein Nielsen, 2017/05/03 05:55:26]

This is another case where `void` as a type parameter would more precisely fix
the problem. We should make a list of these so we can fix them back when that
becomes an option.

[floitsch, 2017/05/03 09:48:11]

Agreed with Lasse: There should at the very least be a TODO. Look at the other
TODOs in the file and add a similar one.

[vsm, 2017/05/03 12:29:56]

Done.

+        if (onError is ZoneBinaryCallback<dynamic, Object, StackTrace>) {
           return self.parent.runBinary(onError, error, stackTrace);
         }
         return self.parent.runUnary(onError, error);