Bug 1629273 - Fix intermittent failure in test_permmanager_load_invalid_entries.js, r=timhuang

Differential Revision: https://phabricator.services.mozilla.com/D70639

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

extensions/permissions/test/unit/test_permmanager_load_invalid_entries.js

@@ -5,6 +5,12 @@ var DEBUG_TEST = false;
 function run_test() {
   // Setup a profile directory.
   var dir = do_get_profile();
+
+  // We need to execute a pm method to be sure that the DB is fully
+  // initialized.
+  var pm = Services.perms;
+  Assert.equal(pm.all.length, 0, "No cookies");
+
   // Get the db file.
   var file = dir.clone();
   file.append("permissions.sqlite");
@@ -220,9 +226,6 @@ function run_test() {
   // This will force the permission-manager to reload the data.
   Services.obs.notifyObservers(null, "testonly-reload-permissions-from-disk");
 
-  // Initialize the permission manager service
-  var pm = Services.perms;
-
   // Let's do something in order to be sure the DB is read.
   Assert.greater(pm.all.length, 0);