Add mastiz@ as owner of chrome/browser/favicon

Change-Id: I1c6d16a6f95beca15c5b00cd84a3057aa9f23441
Bug: None
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2093610Reviewed-by: Peter Kotwicz <pkotwicz@chromium.org>
Commit-Queue: Mikel Astiz <mastiz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#748785}

chrome/browser/favicon/OWNERS

+mastiz@chromium.org
 pkotwicz@chromium.org
 sky@chromium.org