[ddc] Avoid late variables in optimization
[ddc] Avoid late variables in optimization

Hopefully this will avoid bugs in the future if the lowering of
late variables changes.

This does not change the current optimization for late variables
with list literal initializers. That lowering introduces a final
variable that is not marked as late that appears as the receiver
in this logic.

Change-Id: Ib99d0987b166d3f38b60d0dce3fedb166d772e64
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/175444
Reviewed-by: Stephen Adams <60cb5b73b7e0cb7dcda53302da4fab6ecfc7fa8b@google.com>
Commit-Queue: Nicholas Shahan <03847abd2d8aadfe859ecb98095a31f9f515dc47@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