[nnbd_migration] Add api test for how we don't plan to handle postdominators of cfg edits
[nnbd_migration] Add api test for how we don't plan to handle postdominators of cfg edits

Change-Id: I8588297a42584a474508a61c4fb83268da7ab615
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/112757
Commit-Queue: Mike Fairhurst <2002604e76601be549134505841fea93de80dc45@google.com>
Reviewed-by: Paul Berry <72d414e3a99fb120308437779d51667bcc0984eb@google.com>

dart-lang/sdk,dart-archive/dart-sdk,dartino/dart-sdk,dartino/dart-sdk,dartino/dart-sdk,dart-lang/sdk,dartino/dart-sdk,dart-archive/dart-sdk,dartino/dart-sdk,dartino/dart-sdk,dartino/dart-sdk,dart-archive/dart-sdk,dartino/dart-sdk,dart-lang/sdk,dart-archive/dart-sdk,dart-lang/sdk,dart-lang/sdk,dart-archive/dart-sdk,dart-lang/sdk,dart-archive/dart-sdk,dart-lang/sdk,dart-archive/dart-sdk,dart-lang/sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dartino/dart-sdk