Don't pass 'runGuarded' flag to `bindCallback`.

lib/pool.dart

Index: lib/pool.dart
diff --git a/lib/pool.dart b/lib/pool.dart
index 04aaaea6590456dc4267dc1defe36bd6aea2015d..e79f9f807104b05b012faaaed4a30f501e46ea4a 100644
--- a/lib/pool.dart
+++ b/lib/pool.dart
@@ -183,8 +183,7 @@ class Pool {
       _allocatedResources--;
       if (_allocatedResources == 0) _closeGroup.close();
     } else {
-      _onReleaseCallbacks.add(
-          Zone.current.bindCallback(onRelease, runGuarded: false));
+      _onReleaseCallbacks.add(Zone.current.bindCallback(onRelease));
     }
   }