Un-deprecate the CSP child-src directive (#3635)
Un-deprecate the CSP child-src directive (#3635)

Per https://w3c.github.io/webappsec-csp/ (the current CSP spec), the
CSP child-src directive is no longer deprecated.
chrisdavidmills/browser-compat-data,mdn/browser-compat-data,chrisdavidmills/browser-compat-data,mdn/browser-compat-data