Issue 6562 - Remove filter keys from the element hiding code

lib/elemHide.js

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-present 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 142 matching lines @@
 
     // Whitelisting filters
     if (filter instanceof ElemHideException)
     {
       let list = exceptions.get(filter.selector);
       let index = list.indexOf(filter);
       if (index >= 0)
         list.splice(index, 1);
     }
     // Unconditially applied element hiding filters
-    else if (filterBySelector.get(filter.selector) === filter)
+    else if (filterBySelector.get(filter.selector) == filter)
     {
       filterBySelector.delete(filter.selector);
       unconditionalSelectors = null;
     }
     // Conditionally applied element hiding filters
     else
     {
       let domains = filter.domains || defaultDomains;
       for (let domain of domains.keys())
       {
@@ skipping 71 matching lines @@
   getSelectorsForDomain(domain, criteria)
   {
     let selectors = [];
 
     if (typeof criteria == "undefined")
       criteria = ElemHide.ALL_MATCHING;
     if (criteria < ElemHide.NO_UNCONDITIONAL)
       selectors = this.getUnconditionalSelectors();
 
     let specificOnly = (criteria >= ElemHide.SPECIFIC_ONLY);
-    let seenFilters = new Set();
+    let excluded = new Set();
     let currentDomain = domain ? domain.toUpperCase() : "";
+
+    // This code is a performance hot-spot, which is why we've made certain
+    // micro-optimisations. Please be careful before making changes.
     while (true)
     {
       if (specificOnly && currentDomain == "")
         break;
 
       let filters = filtersByDomain.get(currentDomain);
       if (filters)
       {
         for (let [filter, isIncluded] of filters)
         {
-          if (seenFilters.has(filter))
-            continue;
-          seenFilters.add(filter);
-
-          if (isIncluded && !this.getException(filter, domain))
+          if (!isIncluded)
+          {
+            excluded.add(filter);
+          }
+          else if ((excluded.size == 0 || !excluded.has(filter)) &&
+                   !this.getException(filter, domain))
+          {
             selectors.push(filter.selector);
+          }
         }
       }
 
       if (currentDomain == "")
         break;
 
       let nextDot = currentDomain.indexOf(".");
       currentDomain = nextDot == -1 ? "" : currentDomain.substr(nextDot + 1);
     }
 
     return selectors;
   }
 };