::testing::WithParamInterface ends up calling deleting an object
with the type of the template parameter, and the pointer it deletes
could arguably point to a subclass of the param object -- so clang
warns that there's a delete on a class with a virtual method but
without a virtual dtor.  Make the param classes final to let the
compiler know that this can't happen in practice.

BUG=chromium:82385

Change-Id: I49a4120b15670d876613b22ba709d50bf4685006
Reviewed-on: https://chromium-review.googlesource.com/261965Reviewed-by: Jamie Madill <jmadill@chromium.org>
Tested-by: Nico Weber <thakis@chromium.org>