Issue 3840 - Prevent websites from making collapsed elements visible again

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
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  * GNU General Public License for more details.
  *
  * You should have received a copy of the GNU General Public License
  * along with Adblock Plus.  If not, see <http://www.gnu.org/licenses/>.
  */
 
+var MutationObserver = window.MutationObserver || window.WebKitMutationObserver;
 var SELECTOR_GROUP_SIZE = 20;
 
 var typeMap = {
   "img": "IMAGE",
   "input": "IMAGE",
   "picture": "IMAGE",
   "audio": "MEDIA",
   "video": "MEDIA",
   "frame": "SUBDOCUMENT",
   "iframe": "SUBDOCUMENT",
@@ skipping 92 matching lines @@
   {
     if (/^(?!https?:)[\w-]+:/i.test(urls[i]))
       urls.splice(i--, 1);
   }
 
   return urls;
 }
 
 function checkCollapse(element)
 {
-  var tag = element.localName;
-  if (tag in typeMap)
-  {
-    // This element failed loading, did we block it?
-    var urls = getURLsFromElement(element);
-    if (urls.length == 0)
-      return;
+  window.collapsing = true;
 
-    ext.backgroundPage.sendMessage(
+  var mediatype = typeMap[element.localName];
+  if (!mediatype)
+    return;
+
+  var urls = getURLsFromElement(element);
+  if (urls.length == 0)
+    return;
+
+  ext.backgroundPage.sendMessage(
+    {
+      type: "should-collapse",
+      urls: urls,
+      mediatype: mediatype,
+      baseURL: document.location.href
+    },
+
+    function(collapse)
+    {
+      function collapseElement()
       {
-        type: "should-collapse",
-        urls: urls,
-        mediatype: typeMap[tag],
-        baseURL: document.location.href
-      },
+        if (element.localName == "frame")
+          element.style.setProperty("visibility", "hidden", "important");
+        else
+          element.style.setProperty("display", "none", "important");
+      }
 
-      function(response)
+      if (collapse && !element._collapsed)
       {
-        if (response && element.parentNode)
-        {
-          var property = "display";
-          var value = "none";
+        collapseElement();
+        element._collapsed = true;
 
-          // <frame> cannot be removed, doing that will mess up the frameset
-          if (tag == "frame")
-          {
-            property = "visibility";
-            value = "hidden";
-          }
-
-          // <input type="image"> elements try to load their image again
-          // when the "display" CSS property is set. So we have to check
-          // that it isn't already collapsed to avoid an infinite recursion.
-          if (element.style.getPropertyValue(property) != value ||
-              element.style.getPropertyPriority(property) != "important")
-            element.style.setProperty(property, value, "important");
-        }
+        if (MutationObserver)
+          new MutationObserver(collapseElement).observe(
+            element, {
+              attributes: true,
+              attributeFilter: ["style"]
+            }
+          );
       }
-    );
-  }
-
-  window.collapsing = true;
+    }
+  );
 }
 
 function checkSitekey()
 {
   var attr = document.documentElement.getAttribute("data-adblockkey");
   if (attr)
     ext.backgroundPage.sendMessage({type: "add-sitekey", token: attr});
 }
 
 function getContentDocument(element)
@@ skipping 144 matching lines @@
   disconnect: function()
   {
     this.document.removeEventListener("DOMContentLoaded", this.trace);
     this.observer.disconnect();
     clearTimeout(this.timeout);
   }
 };
 
 function reinjectStyleSheetWhenRemoved(document, style)
 {
-  var MutationObserver = window.MutationObserver ||
-                         window.WebKitMutationObserver;
   if (!MutationObserver)
     return null;
 
   var parentNode = style.parentNode;
   var observer = new MutationObserver(function()
   {
     if (style.parentNode != parentNode)
       parentNode.appendChild(style);
   });
 
@@ skipping 203 matching lines @@
   }, true);
 
   return updateStylesheet;
 }
 
 if (document instanceof HTMLDocument)
 {
   checkSitekey();
   window.updateStylesheet = init(document);
 }