Add Apps Foundation OWNERs of default_apps on Chrome OS.

BUG=None

Change-Id: I859ffac541cf895c3317579454ca21bbd8b4593d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1738148
Commit-Queue: Dominick Ng <dominickn@chromium.org>
Reviewed-by: Ben Wells <benwells@chromium.org>
Auto-Submit: Dominick Ng <dominickn@chromium.org>
Cr-Commit-Position: refs/heads/master@{#684293}

chrome/browser/chromeos/extensions/OWNERS

@@ -3,6 +3,11 @@ file://extensions/OWNERS
 # Additional ChromeOS-specific reviewers
 tbarzic@chromium.org
 
+per-file default_app*=dominickn@chromium.org
+per-file default_app*=jshikaram@chromium.org
+per-file default_web_app_ids.h=dominickn@chromium.org
+per-file default_web_app_ids.h=jshikaram@chromium.org
+
 per-file *wallpaper*=file://ash/wallpaper/OWNERS
 
 # input method related reviewers. shuchen@ is primary, and googleo@ is backup.