DDC function type typeTest throws

[eernstg]

DDC in some cases generates code where a typeTest throws rather than returning false when the subtype relationship does not hold. The program is accepted by dartanalyzer --strong n016.dart with no issues.

class A {}
class B extends A {}
class C extends B {}

typedef B F(B b);

C foo(A a) => null;
A bar(C c) => null;

main() {
  print(foo is F); // 'true'.
  print(bar is F); // Throws!
}

When compiling and executing the program using dartdevc.dart from 5982ace, 2017-06-15 14:18:09, ddc n016.dart, the resulting output is as follows:

true

/usr/local/google/home/eernst/devel/dart/work/sdk/pkg/dev_compiler/lib/js/common/dart_sdk.js:9877
          throw e;
          ^
Strong mode is-check failure: (C) -> A does not soundly subtype F((B) -> B)

I would expect bar is F to evaluate to false rather than throwing.

[vsmenon]

This is a dup of #28988 - note, it's currently working as intended. Once dart2js implements strong mode, intent is to of course return false.