Deleting the Google search entry is not an action that can easily be undone, and it will have drastic consequences, such as permanently disabling suggestions and instant for omnibox searches. Creating an alternate entry with the same URL does NOT suffice -- you can't manually enable any of this functionality on the alternate entry.
If you're having this bug, I suggest NOT doing this. Either sit tight until we fix, or if you do create a different entry, KEEP THE ORIGINAL so you can switch back once the fix is out.
--Peter Kasting, Chrome team member and owner of the Omnibox
We used to have a "restore all settings" button that would fix this (among other things), but it disappeared in the preferences UI rewrite and though I've agitated for it to come back, it hasn't.