Add myself to OWNERS

Bug: None
Change-Id: I5ace2a9bdcb2333e03d5b1118747f2b41d74d081
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2618626
Auto-Submit: Collin Baker <collinbaker@chromium.org>
Reviewed-by: Dana Fried <dfried@chromium.org>
Commit-Queue: Dana Fried <dfried@chromium.org>
Cr-Commit-Position: refs/heads/master@{#842446}

chrome/browser/ui/thumbnails/OWNERS

+# Primary
 dfried@chromium.org
+collinbaker@chromium.org
+
+# Backup
 pbos@chromium.org