Add sync tests to mocha suite

src/js/background/assignManager.js

@@ -1,4 +1,4 @@
-const assignManager = {
+window.assignManager = {
   MENU_ASSIGN_ID: "open-in-this-container",
   MENU_REMOVE_ID: "remove-open-in-this-container",
   MENU_SEPARATOR_ID: "separator",

src/js/background/identityState.js

@@ -1,4 +1,4 @@
-const identityState = {
+window.identityState = {
   storageArea: {
     area: browser.storage.local,
 

src/js/background/sync.js

@@ -1,6 +1,6 @@
 const SYNC_DEBUG = true;
 
-const sync = {
+window.sync = {
   storageArea: {
     area: browser.storage.sync,