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

firstRun.js

 var backgroundPage = chrome.extension.getBackgroundPage();
 var require = backgroundPage.require;
 var Prefs = require("prefs").Prefs;
 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("");
   setLinks("title-changelog", "https://adblockplus.org/releases/adblock-plus-" + versionId + "-for-google-chrome-released");
   setLinks("acceptableAdsExplanation", getDocLink("acceptable_ads", "criteria"),
@@ skipping 33 matching lines @@
     }
   }
 }
 
 function getDocLink(page, anchor)
 {
   return Prefs.documentation_link
               .replace(/%LINK%/g, page)
               .replace(/%LANG%/g, Utils.appLocale) + (anchor ? "#" + anchor : "");
 }