Issue 4795 - Use modern JavaScript syntax

ext/background.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 nonEmptyPageMaps = Object.create(null);
   let pageMapCounter = 0;
 
   let PageMap = ext.PageMap = function()
   {
     this._map = Object.create(null);
     this._id = ++pageMapCounter;
   };
   PageMap.prototype = {
-    _delete: function(id)
+    _delete(id)
     {
       delete this._map[id];
 
       if (Object.keys(this._map).length == 0)
         delete nonEmptyPageMaps[this._id];
     },
-    keys: function()
+    keys()
     {
       return Object.keys(this._map).map(ext.getPage);
     },
-    get: function(page)
+    get(page)
     {
       return this._map[page.id];
     },
-    set: function(page, value)
+    set(page, value)
     {
       this._map[page.id] = value;
       nonEmptyPageMaps[this._id] = this;
     },
-    has: function(page)
+    has(page)
     {
       return page.id in this._map;
     },
-    clear: function()
+    clear()
     {
       for (let id in this._map)
         this._delete(id);
     },
-    delete: function(page)
+    delete(page)
     {
       this._delete(page.id);
     }
   };
 
   ext._removeFromAllPageMaps = pageId =>
   {
     for (let pageMapId in nonEmptyPageMaps)
       nonEmptyPageMaps[pageMapId]._delete(pageId);
   };
 }