[ddc] Compare types with new DartTypeEquivalence
[ddc] Compare types with new DartTypeEquivalence

Avoids an assertion failure in the front end.

Change-Id: I7994fa611f82011857750cc60af64a2c89c96bf7
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/152923
Reviewed-by: Dmitry Stefantsov <95a4b7e39916a54bd6477bec6a6de014b977db32@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