Settings WebUI: Add ChromeOS OWNERs for multidevice_page/

Bug: None
Change-Id: I15ad232b6e8bff08df4fd701db7f23be13fbb053
Reviewed-on: https://chromium-review.googlesource.com/1238993
Commit-Queue: Demetrios Papadopoulos <dpapad@chromium.org>
Reviewed-by: Kyle Horimoto <khorimoto@chromium.org>
Reviewed-by: Jeremy Klein <jlklein@chromium.org>
Cr-Commit-Position: refs/heads/master@{#593275}

chrome/browser/resources/settings/multidevice_page/OWNERS

+file://chromeos/services/multidevice_setup/OWNERS
+
+# COMPONENT: UI>Settings

chrome/browser/ui/webui/settings/chromeos/OWNERS

+per-file multidevice_handler*=file://chromeos/services/multidevice_setup/OWNERS
+
+# COMPONENT: UI>Settings