Issue 4795 - Use modern JavaScript syntax

include.preload.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";
 
-let typeMap = {
+const typeMap = {
   "img": "IMAGE",
   "input": "IMAGE",
   "picture": "IMAGE",
   "audio": "MEDIA",
   "video": "MEDIA",
   "frame": "SUBDOCUMENT",
   "iframe": "SUBDOCUMENT",
   "object": "OBJECT",
   "embed": "OBJECT"
 };
@@ skipping 44 matching lines @@
   }
 
   return urls;
 }
 
 function getURLsFromMediaElement(element)
 {
   let urls = getURLsFromAttributes(element);
 
   for (let child of element.children)
+  {
     if (child.localName == "source" || child.localName == "track")
       urls.push.apply(urls, getURLsFromAttributes(child));
+  }
 
   if (element.poster)
     urls.push(element.poster);
 
   return urls;
 }
 
 function getURLsFromElement(element)
 {
   let urls;
@@ skipping 475 matching lines @@
       checkLoaded();
     });
   }
 };
 
 if (document instanceof HTMLDocument)
 {
   checkSitekey();
   wrapWebSocket();
 
-  let elemhide = new ElemHide();
+  // This variable is also used by our other content scripts, outside of the
+  // current scope.
+  var elemhide = new ElemHide();
   elemhide.apply();
 
   document.addEventListener("error", event =>
   {
     checkCollapse(event.target);
   }, true);
 
   document.addEventListener("load", event =>
   {
     let element = event.target;
     if (/^i?frame$/.test(element.localName))
       checkCollapse(element);
   }, true);
 }