Bug 1579489 - Check the persistent permission checkbox by default for WebExtension WebRTC prompts. r=jib

This is done to offset the requirement that extensions have to get persistent permission before
they can start using WebRTC in popups.

Differential Revision: https://phabricator.services.mozilla.com/D45335

--HG--
extra : moz-landing-system : lando

browser/modules/webrtcUI.jsm

@@ -1156,6 +1156,7 @@ function prompt(aBrowser, aRequest) {
 
     options.checkbox = {
       label: stringBundle.getString("getUserMedia.remember"),
+      checked: principal.isAddonOrExpandedAddonPrincipal,
       checkedState: reasonForNoPermanentAllow
         ? {
             disableMainAction: true,