Adds some basic tests to check for runtime subtyping with JS
interop types. Uses function types only to check for subtyping
relationships. Extends some tests on is and as checks as well.
Change-Id: I9cbc91d0c475fba3213dd9a3443921232c286804
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/170660
Commit-Queue: Srujan Gaddam <srujzs@google.com>
Reviewed-by: Sigmund Cherem <sigmund@google.com>
Srujan Gaddam