tree cd4825ff88777d6fba5f94ff95d69f4719a93072
parent 407378879bfd689d8a91d27e6ad8885fa0c6034f
author Paul Berry <paulberry@google.com> 1556714534 +0000
committer commit-bot@chromium.org <commit-bot@chromium.org> 1556714534 +0000

Make each NullabilityNode track those nodes that are downstream of it.

This allows more migration tool unit tests to be simplified so that
they don't have to refer to ConstraintVariable objects directly
anymore.

In order to make this work, a few other changes were also necessary:

- Make a derived class for NullabilityNodes that arise from
  conditional expressions.

- Add a getter to reveal whether a NullabilityNode is known a priori
  to be non-nullable.

Change-Id: I8a68b627ce9e807a50d371369985f52848903a2f
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/100922
Commit-Queue: Paul Berry <paulberry@google.com>
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>
Reviewed-by: Konstantin Shcheglov <scheglov@google.com>