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>
diff --git a/tools/valgrind.supp b/tools/valgrind.supp
index 601b3a7..d0640fe 100644
--- a/tools/valgrind.supp
+++ b/tools/valgrind.supp
@@ -4,7 +4,7 @@
 {
    nanobench_and_dm_keepalive_thread_leak
    Memcheck:Leak
-   match-leak-kinds: possible
+   match-leak-kinds: possible,definite
    ...
    fun:_ZN8SkThreadC1EPFvPvES0_
    ...