Add OWNERS for components/keep_alive_registry

Rationale for owner choices: keep-alive seem mostly related to browser
UI and Chrome apps. I eliminated OWNERS from chrome/browser/ui who were
already listed in >20 OWNERS files.

Bug: None
Change-Id: I4769e2c5dafc809d500b1e71669decfd745adda6
Reviewed-on: https://chromium-review.googlesource.com/1086303Reviewed-by: Colin Blundell <blundell@chromium.org>
Reviewed-by: Michael Giuffrida <michaelpg@chromium.org>
Reviewed-by: Ben Wells <benwells@chromium.org>
Commit-Queue: Michael Giuffrida <michaelpg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#564961}

components/keep_alive_registry/OWNERS

+benwells@chromium.org
+michaelpg@chromium.org