One test verifies that the default values of fromEnvironment
constructors are the values false/0/''.
The other new test verifies that it is allowed to invoke an expression
whose static type is a proper subtype of a function type (X extends F,
where F is a function type), cf.
https://github.com/dart-lang/language/issues/896.
Change-Id: I4ee32df7c5950be07b800027f000a486bf3af61c
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/141249
Commit-Queue: Erik Ernst <eernst@google.com>
Reviewed-by: Lasse R.H. Nielsen <lrn@google.com>
