Add ajuma@ to ios/web/navigation OWNERS.

Ali fixed a number of complex navigation bugs and has very deep
understanding of WebKit navigation code.

Bug: None
Change-Id: Ia7d16605c1434812210a835b0fb97c9cd6deff37
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1663364
Auto-Submit: Eugene But <eugenebut@chromium.org>
Reviewed-by: Kurt Horimoto <kkhorimoto@chromium.org>
Commit-Queue: Kurt Horimoto <kkhorimoto@chromium.org>
Cr-Commit-Position: refs/heads/master@{#670156}

ios/web/navigation/OWNERS

+ajuma@chromium.org
 danyao@chromium.org
 eugenebut@chromium.org
 kkhorimoto@chromium.org