Issue 5773 - use ES6 for stylesheets and cssRules.

lib/content/elemHideEmulation.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 393 matching lines @@
 
     let elements = [];
     let elementFilters = [];
 
     let cssStyles = [];
 
     let stylesheetOnlyChange = !!stylesheets;
     if (!stylesheets)
       stylesheets = this.document.styleSheets;
 
-    // Chrome < 51 doesn't have an iterable StyleSheetList
-    // https://issues.adblockplus.org/ticket/5381
-    for (let i = 0; i < stylesheets.length; i++)
+    for (let stylesheet of stylesheets)
     {
-      let stylesheet = stylesheets[i];
       // Explicitly ignore third-party stylesheets to ensure consistent behavior
       // between Firefox and Chrome.
       if (!this.isSameOrigin(stylesheet))
         continue;
 
       let rules = stylesheet.cssRules;
       if (!rules)
         continue;
 
-      // Chrome < 51 doesn't have an iterable CSSRuleList
-      // https://issues.adblockplus.org/ticket/5773
-      for (let j = 0; j < rules.length; j++)
+      for (let rule of rules)
       {
-        let rule = rules[j];
         if (rule.type != rule.STYLE_RULE)
           continue;
 
         cssStyles.push(stringifyStyle(rule));
       }
     }
 
     let patterns = this.patterns.slice();
     let pattern = null;
     let generator = null;
@@ skipping 154 matching lines @@
           characterData: true,
           subtree: true
         }
       );
       this.document.addEventListener("load", this.onLoad.bind(this), true);
     }
   }
 };
 
 exports.ElemHideEmulation = ElemHideEmulation;