[benchmarks/nnbd] Fix NNBD compile-time errors in benchmarks/Calls
[benchmarks/nnbd] Fix NNBD compile-time errors in benchmarks/Calls

Fixes compile-time errors in vm/dart/async_igoto_threshold_flag_test
which uses Calls benchmark.

Change-Id: I1e3d075bb7f40516c5319e4eb4ebf7dc5b2c7ccb
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/146700
Reviewed-by: Liam Appelbe <78c2029e58e395825ba7228e218c841bb436a9e9@google.com>
Reviewed-by: Régis Crelier <c2bf536a10d9f2530c38e4e8da517718be8c39ce@google.com>
Commit-Queue: Alexander Markov <239e774fd29abc1267878f57afe1a8a03e0ca887@google.com>

dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk