owners: Add brucedawson@, robliao@, sky@ to ui/base/win

BUG=none

Change-Id: I62430a543623f957a7be1bc197b05978cc1bce76
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1543457
Commit-Queue: Sadrul Chowdhury <sadrul@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Reviewed-by: Robert Liao <robliao@chromium.org>
Cr-Commit-Position: refs/heads/master@{#645370}

ui/base/win/OWNERS

+brucedawson@chromium.org
+robliao@chromium.org
+sky@chromium.org