[benchmark] Test dart2js sound nullability options.
[benchmark] Test dart2js sound nullability options.

Change-Id: Ie548ad57094cd334b95d1c49f2a8f02ce762f56f
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/153207
Reviewed-by: Alexander Thomas <29642742b6693024c89de8232f2e2542cf7eedf7@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