Adds robliao to ui/shell_dialogs owners

BUG=none
TEST=none

Change-Id: If6677be34230f148b0299739325992a174c339ac
Reviewed-on: https://chromium-review.googlesource.com/c/1279235Reviewed-by: Robert Liao <robliao@chromium.org>
Commit-Queue: Scott Violet <sky@chromium.org>
Cr-Commit-Position: refs/heads/master@{#599383}

ui/shell_dialogs/OWNERS

 per-file *android*=miguelg@chromium.org
 per-file *android*=qinmin@chromium.org
+
+per-file *win*=robliao@chromium.org