GitLab

Create OKButton shared matcher, since this button is likely used
other places.

Bug: 
Change-Id: Ib45265f6be2ebc2d59f3e912bc4d6e6fb628771d
Reviewed-on: https://chromium-review.googlesource.com/503493Reviewed-by: Eugene But <eugenebut@chromium.org>
Commit-Queue: Mike Baxley <baxley@chromium.org>
Cr-Commit-Position: refs/heads/master@{#471126}