Issue 5161 - Use maps and sets where appropriate

lib/whitelisting.js

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-2017 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
@@ skipping 110 matching lines @@
  * @return {string}
  */
 exports.getKey = (page, frame) =>
 {
   let keys = sitekeys.get(page);
   if (!keys)
     return null;
 
   for (; frame != null; frame = frame.parent)
   {
-    let key = keys[stringifyURL(frame.url)];
+    let key = keys.get(stringifyURL(frame.url));
     if (key)
       return key;
   }
 
   return null;
 };
 
 function checkKey(token, url)
 {
   let parts = token.split("_");
   if (parts.length < 2)
     return false;
 
   let key = parts[0].replace(/=/g, "");
   let signature = parts[1];
   let data = url.pathname + url.search + "\0" +
              url.host + "\0" +
              window.navigator.userAgent;
   if (!verifySignature(key, signature, data))
     return false;
 
   return key;
 }
 
 function recordKey(key, page, url)
 {
   let keys = sitekeys.get(page);
   if (!keys)
   {
-    keys = Object.create(null);
+    keys = new Map();
     sitekeys.set(page, keys);
   }
-  keys[stringifyURL(url)] = key;
+  keys.set(stringifyURL(url), key);
 }
 
 port.on("filters.addKey", (message, sender) =>
 {
   let key = checkKey(message.token, sender.frame.url);
   if (key)
     recordKey(key, sender.page, sender.frame.url);
 });
 
 function onHeadersReceived(details)
@@ skipping 19 matching lines @@
 {
   chrome.webRequest.onHeadersReceived.addListener(
     onHeadersReceived,
     {
       urls: ["http://*/*", "https://*/*"],
       types: ["main_frame", "sub_frame"]
     },
     ["responseHeaders"]
   );
 }