Issue 4298 - Enforce 'display: none' for ElemHide

include.preload.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
@@ skipping 329 matching lines @@
     return null;
 
   var rules = style.sheet.rules;
   var parentNode = style.parentNode;
   var observer = new MutationObserver(function()
   {
     if (style.parentNode != parentNode)
     {
       parentNode.appendChild(style);
 
+      // Our style element's sheet is sometimes lost when the element is removed
+      // from the DOM. A new empty sheet is then created in its place so we have
+      // to restore the rules ourselves.
       if (style.sheet.rules.length == 0)
       {
         for (var i = 0; i < rules.length; i += 1)
           style.sheet.addRule(rules[i].selectorText, "display: none !important;");
 
         style.id = id;
         injectJS(
           function(id)
           {
             var style = document.getElementById(id) ||
                         document.documentElement.shadowRoot.getElementById(id);
             style.removeAttribute("id");
+
             Object.defineProperty(style.sheet, "disabled",
                                   {value: false, enumerable: true});
           }, id
         );
       }
     }
   });
 
   observer.observe(parentNode, {childList: true});
   return observer;
@@ skipping 15 matching lines @@
 function protectStyleSheet(document, style)
 {
   style.id = id;
 
   var protector = function(id)
   {
     var style = document.getElementById(id) ||
                 document.documentElement.shadowRoot.getElementById(id);
     style.removeAttribute("id");
 
-    var i;
-    var disableables = [style, style.sheet];
-    for (i = 0; i < disableables.length; i += 1)
-      Object.defineProperty(disableables[i], "disabled",
-                            {value: false, enumerable: true});
+    Object.defineProperty(style, "disabled",
+                          {value: false, enumerable: true});
+    Object.defineProperty(style.sheet, "disabled",
+                          {value: false, enumerable: true});
 
-    var methods = ["deleteRule", "removeRule"];
-    for (i = 0; i < methods.length; i += 1)
+    function wrapMethods(methodNames, descKey, defaultReturnValue)
     {
-      if (methods[i] in CSSStyleSheet.prototype)
+      for (var i = 0; i < methodNames.length; i += 1)
       {
-        (function(method)
+        if (methodNames[i] in CSSStyleSheet.prototype)
         {
-          var original = CSSStyleSheet.prototype[method];
-          CSSStyleSheet.prototype[method] = function(index)
+          (function(method)
           {
-            if (this != style.sheet)
-              original.call(this, index);
-          };
-        }(methods[i]));
+            var desc = Object.getOwnPropertyDescriptor(CSSStyleSheet.prototype,
+                                                       method);
+            var original = desc[descKey];
+            desc[descKey] = function()
+            {
+              if (this != style.sheet)
+                return original.apply(this, arguments);
+              return defaultReturnValue;
+            };
+            Object.defineProperty(CSSStyleSheet.prototype, method, desc);
+          }(methodNames[i]));
+        }
       }
     }
+
+    wrapMethods(["deleteRule", "removeRule"], "value");
+    wrapMethods(["rules", "cssRules"], "get", []);
   };
 
   injectJS(protector, id);
 }
 
 // Neither Chrome[1] nor Safari allow us to intercept WebSockets, and therefore
 // some ad networks are misusing them as a way to serve adverts and circumvent
 // us. As a workaround we wrap WebSocket, preventing blocked WebSocket
 // connections from being opened.
 // [1] - https://bugs.chromium.org/p/chromium/issues/detail?id=129353
@@ skipping 256 matching lines @@
   }, true);
 
   return updateStylesheet;
 }
 
 if (document instanceof HTMLDocument)
 {
   checkSitekey();
   window.updateStylesheet = init(document);
 }