Update Valgrind match-leak-kinds for keep-alive thread.

Update Valgrind match-leak-kinds for keep-alive thread.

Valgrind has tipped over from seeing the keep-alive thread as possibly
leaked to seeing it as definitely leaked.  We can suppress both.

An alternative here is "all" or to just remove the line.  For the moment
I think this is best, as we're still excluding indirect leaks this way.
I'd want to think a bit whether it made sense for the keep-alive thread
to indirectly leak anything, so I'd like it to fail if it comes up.

Change-Id: Ib28790a1d84a0a9061fdb6de48569ca8ea51b52a
Reviewed-on: https://skia-review.googlesource.com/8764
Reviewed-by: Brian Salomon <bsalomon@google.com>
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Mike Klein <mtklein@chromium.org>