Issue 6727 - Use string rather than map for single-domain filters

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 54 matching lines @@
  */
 let exceptions = new Map();
 
 /**
  * Adds a filter to the lookup table of filters by domain.
  * @param {Filter} filter
  */
 function addToFiltersByDomain(filter)
 {
   let domains = filter.domains || defaultDomains;
+
+  if (typeof domains == "string")

[sergei, 2018/05/28 09:22:07]

Will the refactoring of that `typeof DOMAINS == "string"` with the applying of
an action for each domain significantly negatively affect performance and the
memory usage?

I'm also not a big fan of spreading the logic
let defaultDomains = new Map([["", true]]);
and
domains = [[domains, true]];
among files, IMO it would be better to keep it in filter classes.

[kzar, 2018/06/05 16:51:30]

Agreed, if possible (without messing up performance / memory usage) that would
be nice.

+    domains = [[domains, true]];
+
   for (let [domain, isIncluded] of domains)
   {
     // There's no need to note that a filter is generically disabled.
     if (!isIncluded && domain == "")
       continue;
 
     let filters = filtersByDomain.get(domain);
     if (!filters)
       filtersByDomain.set(domain, filters = new Map());
     filters.set(filter, isIncluded);
@@ skipping 96 matching lines @@
     // Unconditially applied element hiding filters
     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())
+
+      if (typeof domains == "string")
+        domains = [[domains]];
+
+      for (let [domain] of domains)
       {
         let filters = filtersByDomain.get(domain);
         if (filters)
           filters.delete(filter);
       }
     }
 
     knownFilters.delete(filter);
     FilterNotifier.emit("elemhideupdate");
   },
@@ skipping 64 matching lines @@
       let nextDot = currentDomain.indexOf(".");
       currentDomain = nextDot == -1 ? "" : currentDomain.substr(nextDot + 1);
     }
 
     if (!specificOnly)
       selectors = getUnconditionalSelectors().concat(selectors);
 
     return selectors;
   }
 };