Test the polymorphic behavior of this utility.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@194320 91177308-0d34-0410-b5e6-96231b3b80d8
Switch to allow implicit construction. In many cases, we're wrapping
a derived type and this makes it *much* easier to write this code.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@194321 91177308-0d34-0410-b5e6-96231b3b80d8