Update OWNERS for src/debug and src/snapshot

R=jgruber@chromium.org, verwaest@chromium.org

Change-Id: I5b607e9c121accafff0c65fc74b073a873f749af
Reviewed-on: https://chromium-review.googlesource.com/721665Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Commit-Queue: Yang Guo <yangguo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48807}

src/debug/OWNERS

 set noparent
 
 bmeurer@chromium.org
+franzih@chromium.org
 jgruber@chromium.org
 mvstanton@chromium.org
-ulan@chromium.org
 verwaest@chromium.org
 yangguo@chromium.org
 

src/snapshot/OWNERS

 set noparent
 
 jgruber@chromium.org
+petermarshall@chromium.org
 verwaest@chromium.org
 yangguo@chromium.org