pkg/front_end/testcases/runtime_checks_new/contravariant_combiner.dart:22:50: Context: Write to b@535
  b /*@ checkReturn=B<num*, (num*) ->* void>* */ += 1;
                                                 ^^
pkg/front_end/testcases/runtime_checks_new/contravariant_combiner.dart:23:58: Context: Write to b@535
  var x = b /*@ checkReturn=B<num*, (num*) ->* void>* */ += 2;
                                                         ^^