Computer Configuration > Administrative Templates > Google Chrome > Default search provider
Both
HKLM\Software\Policies\Google\Chrome
If DefaultSearchProviderEnabled is on, then setting DefaultSearchProviderSearchURLPostParams specifies the parameters when searching a URL with POST. It consists of comma-separated, name-value pairs. If a value is a template parameter, such as '{searchTerms}', real search terms data replaces it. Leaving DefaultSearchProviderSearchURLPostParams unset means search requests are sent using the GET method. Example value: q={searchTerms},ie=utf-8,oe=utf-8