Issue 3699 - Patch DOM API in order to prevent disabling the injected stylesheet

include.preload.js

Index: include.preload.js
===================================================================
--- a/include.preload.js
+++ b/include.preload.js
@@ -331,61 +331,78 @@
   }
 };
 
-function reinjectRulesWhenRemoved(document, style)
+function runInPage(document, arg, fn)
 {
-  var MutationObserver = window.MutationObserver || window.WebKitMutationObserver;
-  if (!MutationObserver)
-    return;
+  var script = document.createElement("script");
+  script.async = false;
+  script.textContent = "(" + fn + ")(" + arg + ");";
+  document.documentElement.appendChild(script);
+  document.documentElement.removeChild(script);
+}
 
-  var observer = new MutationObserver(function(mutations)
+function protectStylesheet(document, style)
+{
+  var id = Math.random().toString(36).substr(2);
+  style.id = id;
+
+  runInPage(document, '"' + id + '"', function(id)
   {
-    var isStyleRemoved = false;
-    for (var i = 0; i < mutations.length; i++)
+    var style = document.getElementById(id) ||
+                document.documentElement.shadowRoot.getElementById(id);
+    style.removeAttribute("id");
+
+    var removeChild = Node.prototype.removeChild;
+    Node.prototype.removeChild = function(child)
     {
-      if ([].indexOf.call(mutations[i].removedNodes, style) != -1)
+      if (child != style)
+        removeChild.call(this, child);
+    };
+
+    var remove = Element.prototype.remove;
+    if (remove)
+      Element.prototype.remove = function()
       {
-        isStyleRemoved = true;
-        break;
+        if (this != style)
+          remove.call(this);
+      };
+
+    var deleteRule = CSSStyleSheet.prototype.deleteRule;
+    CSSStyleSheet.prototype.deleteRule = function(index)
+    {
+      if (this != style.sheet)
+        deleteRule.call(this, index);
+    };
+
+    var removeRule = CSSStyleSheet.prototype.removeRule;
+    if (removeRule)
+      CSSStyleSheet.prototype.removeRule = function(index)
+      {
+        if (this != style.sheet)
+          removeRule.call(this, index);
+      };
+
+    Object.defineProperty(
+      style, 'disabled',
+      {
+        value: false,
+        enumerable: true
       }
-    }
-    if (!isStyleRemoved)
-      return;
+    );
 
-    observer.disconnect();
-
-    var n = document.styleSheets.length;
-    if (n == 0)
-      return;
-
-    var stylesheet = document.styleSheets[n - 1];
-    ext.backgroundPage.sendMessage(
-      {type: "get-selectors"},
-
-      function(response)
+    Object.defineProperty(
+      style.sheet, 'disabled',
       {
-        var selectors = response.selectors;
-        while (selectors.length > 0)
-        {
-          var selector = selectors.splice(0, SELECTOR_GROUP_SIZE).join(", ");
-
-          // Using non-standard addRule() here. This is the only way
-          // to add rules at the end of a cross-origin stylesheet
-          // because we don't know how many rules are already in there
-          stylesheet.addRule(selector, "display: none !important;");
-        }
+        value: false,
+        enumerable: true
       }
     );
   });
-
-  observer.observe(style.parentNode, {childList: true});
-  return observer;
 }
 
 function init(document)
 {
   var shadow = null;
   var style = null;
-  var observer = null;
   var tracer = null;
   var propertyFilters = new CSSPropertyFilters(window, addElemHideSelectors);
 
@@ -424,7 +441,7 @@
       if (!style.sheet)
         return;
 
-      observer = reinjectRulesWhenRemoved(document, style);
+      protectStylesheet(document, style);
     }
 
     // If using shadow DOM, we have to add the ::content pseudo-element
@@ -461,10 +478,6 @@
       if (!selectors || !CSSPropertyFiltersLoaded)
         return;
 
-      if (observer)
-        observer.disconnect();
-      observer = null;
-
       if (tracer)
         tracer.disconnect();
       tracer = null;