Bug 1553265 - add a document.addCertException function to about:certerror pages and use it there; also treat GeckoView error pages as CallerIsTrusted(Net|Cert)Error; r=snorp,johannh,baku

Add a document.addCertException function to about:certerror pages, and use it on the desktop certerror page.

Also, as the CallerIsTrusted* functions expect URLs like about:certerror, but GeckoView error pages are data URLs, and so need to be handled differently for these special error-page methods to be exposed on their documents.

Example usage of document.addCertException:
  document.addCertException(
    true|false /* true == temporary, false == permanent */
  ).then(
    () => {
      location.reload();
    },
    err => {
      console.error(err);
    }
  );

Differential Revision: https://phabricator.services.mozilla.com/D56974

browser/base/content/aboutNetError.js

@@ -511,7 +511,15 @@ function initPageCertError() {
 }
 
 function addCertException() {
-  RPMSendAsyncMessage("AddCertException", { location: document.location.href });
+  const isPermanent =
+    !RPMIsWindowPrivate() &&
+    RPMGetBoolPref("security.certerrors.permanentOverride");
+  document.addCertException(!isPermanent).then(
+    () => {
+      location.reload();
+    },
+    err => {}
+  );
 }
 
 function onReturnButtonClick(e) {