Issue 4871 - Start using ESLint for adblockplusui

ext/content.js

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-2016 Eyeo GmbH
  *
  * Adblock Plus is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 3 as
  * published by the Free Software Foundation.
  *
  * Adblock Plus is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  * GNU General Public License for more details.
  *
  * You should have received a copy of the GNU General Public License
  * along with Adblock Plus.  If not, see <http://www.gnu.org/licenses/>.
  */
 
 "use strict";
 
+(function()
 {
   if (typeof ext == "undefined")
     window.ext = {};
 
   let backgroundFrame = document.createElement("iframe");
   backgroundFrame.setAttribute("src",
                                "background.html" + window.location.search);
   backgroundFrame.style.display = "none";
   window.addEventListener("DOMContentLoaded", () =>
   {
@@ skipping 44 matching lines @@
               event.data.messageId == messageId)
           {
             window.removeEventListener("message", callbackWrapper, false);
             responseCallback(event.data.payload);
           }
         };
         window.addEventListener("message", callbackWrapper, false);
       }
     }
   };
-}
+}());