Replaced chrome.i18n by a platform-independent i18n object in UI

firstRun.js

Index: firstRun.js
===================================================================
--- a/firstRun.js
+++ b/firstRun.js
@@ -6,17 +6,17 @@ var Utils = require("utils").Utils;
 function init()
 {
   // Choose a share text variant randomly
   var variant = Math.floor(Math.random() * 2) + 1;
   document.documentElement.setAttribute("share-variant", variant);
 
   // Set up page title
   var titleId = (backgroundPage.isFirstRun ? "firstRun_title_install" : "firstRun_title_update");
-  var pageTitle = chrome.i18n.getMessage(titleId);
+  var pageTitle = i18n.getMessage(titleId);
   document.title = document.getElementById("title-main").textContent = pageTitle;
 
   // Only show changelog link on the update page
   if (backgroundPage.isFirstRun)
     document.getElementById("title-changelog").style.display = "none";
 
   // Set up URLs
   var versionId = chrome.app.getDetails().version.split(".").slice(0, 2).join("");