Add japhet to public/OWNERS.

https://groups.google.com/a/chromium.org/forum/#!topic/blink-dev/StkI3k4Pm5U
saw multiple calls for more public/OWNERS. I volunteer as tribute.

"git shortlog -s -n public/" says I've been the 5th most frequent committer to
public/ in the last 18 months with 38 changes.

BUG=

Review URL: https://codereview.chromium.org/646783002

git-svn-id: svn://svn.chromium.org/blink/trunk@183550 bbb929c8-8fbe-4397-9dbb-9b2b20218538