Before landing, two issues to resolve:
(1) We appear to allow sideways casts now without static error - e.g.,
List<Object> -> FutureOr<List<String>>
Is that intended? If so, it breaks an assumption that implicit casts
are from supertype to subtype.
(2) LUB and FutureOr
It appears that the LUB of, e.g., String and Future<String> is Object.
See fixes in tests to record casts back to FutureOr.
Fixes#29251R=leafp@google.com
Review-Url: https://codereview.chromium.org/2801683004 .
Vijay Menon
bc3089838c