Bug 1727820 - Implement nsIUpdateChecker API change r=bhearsum

Note that, for the most part, this isn't meant to change behavior. It is just meant to eliminate race conditions and fix some bugs. However, a tiny bit of behavior has been changed.

Previously, the fallback error codes used to potentially populate nsIUpdate.statusText were 200 in Checker.onError (corresponding to "Update XML file malformed") and 404 in Checker.onLoad (corresponding to "Update XML file not found"). These really seem backwards to me. Especially in the Checker.onLoad case, where we basically use that as the fallback if we fail to parse the update XML. So the codes have effectively been reversed in this patch.

Differential Revision: https://phabricator.services.mozilla.com/D159302

toolkit/locales/en-US/chrome/mozapps/update/updates.properties

@@ -41,3 +41,5 @@ check_error-2152398920=Proxy server connection refused
 check_error-2153390069=Server certificate has expired (please adjust your system clock to the correct date and time if it is incorrect)
 check_error-verification_failed=The integrity of the update could not be verified
 check_error-move_failed=Failed to prepare the update for installation
+check_error-update_url_not_available=Update URL not available
+check_error-connection_aborted=Connection aborted

toolkit/mozapps/update/components.conf

@@ -23,7 +23,7 @@ Classes = [
         'cid': '{898CDC9B-E43F-422F-9CC4-2F6291B415A3}',
         'contract_ids': ['@mozilla.org/updates/update-checker;1'],
         'jsm': 'resource://gre/modules/UpdateService.jsm',
-        'constructor': 'Checker',
+        'constructor': 'CheckerService',
         'singleton': True,
     },