Add ichikawa@ as an owner of //tools/licenses.py.

Currently there is no owner of this file since both of the original
owners removed themselves from OWNERS. It is not great since all CLs to
this file must be reviewed by one of //tools/OWNERS.

So I'm nominating myself has an owner. I'm not really an expert of this
file, but I have made several edits to this file and may be relatively
knowledgeable about this file.

One concern is that I'm not a full-time Chromium developer, so I might
give up later if I found it takes my time too much to be an owner. But
let me give a try.

yipengw@ mef@ (who recently edited this file as well): Feel free to
nominate yourselves as owners as well if you are happy with it. I guess
having multiple owners is preferred.

Bug: 
Change-Id: Id5ba3f2ce1c0414de2342993b56962aa31803937
Reviewed-on: https://chromium-review.googlesource.com/861379
Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Commit-Queue: Hiroshi Ichikawa <ichikawa@chromium.org>
Cr-Commit-Position: refs/heads/master@{#528856}

• tools/OWNERS[diff]
• tools/tests/OWNERS[Added - diff]