We cannot assign a meaningful type to Promise#catch() or
Promise#finally(), since they both return whatever the invocation of
'then' on the receiver returns, and that is monkeypatchable by arbitrary
user JavaScript.

Bug: chromium:908309, v8:7253
Change-Id: Ib15f81c366938a1b1f10be6c6af85c1f3374b898
Reviewed-on: https://chromium-review.googlesource.com/c/1350789Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Commit-Queue: Benedikt Meurer <bmeurer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#57828}