Add OWNERS to //chrome/test/data/webui/settings/chromeos

https://chromium-review.googlesource.com/c/chromium/src/+/1719450 added
//chrome/browser/resources/settings/chromeos/

This adds the same people to OWNERS for tests of the above code.

Bug: 987786
Change-Id: I4dd698aceb690c551c95d5bfbb24fa4fe40b2015
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1720747Reviewed-by: Demetrios Papadopoulos <dpapad@chromium.org>
Reviewed-by: Jordy Greenblatt <jordynass@chromium.org>
Reviewed-by: May Lippert <maybelle@chromium.org>
Commit-Queue: James Cook <jamescook@chromium.org>
Cr-Commit-Position: refs/heads/master@{#681854}

chrome/test/data/webui/settings/OWNERS

 file://chrome/browser/resources/settings/OWNERS
 
+per-file split_settings_flag_test.js=file://chrome/browser/resources/settings/chromeos/OWNERS
+
 # COMPONENT: UI>Settings

chrome/test/data/webui/settings/chromeos/OWNERS

+file://chrome/browser/resources/settings/chromeos/OWNERS
+
+# COMPONENT: OS>Systems>Settings