Add tmartino as OWNER of //components/autofill

Per discussions with ftirelo@ about ensuring sufficient OWNERS coverage
among current team members, I'm requesting to be added as an OWNER of
this directory.

Change-Id: Idc8a68bfced50ae9e371e3b899f9958bdbd4c41c
Reviewed-on: https://chromium-review.googlesource.com/c/1489898Reviewed-by: Fabio Tirelo <ftirelo@chromium.org>
Commit-Queue: Fabio Tirelo <ftirelo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#635739}

components/autofill/OWNERS

@@ -4,5 +4,6 @@ ftirelo@chromium.org
 mahmadi@chromium.org
 rogerm@chromium.org
 sebsg@chromium.org
+tmartino@chromium.org
 
 # COMPONENT: UI>Browser>Autofill