Issue 4191 - Restore rules for reinjected stylesheets

include.preload.js

Index: include.preload.js
diff --git a/include.preload.js b/include.preload.js
index f4ab60be781c88c27079d7df6f1c4e77a430188d..0397c82c7a0036d8774807f2013f9b9dd04470be 100644
--- a/include.preload.js
+++ b/include.preload.js
@@ -334,32 +334,53 @@ ElementHidingTracer.prototype = {
   }
 };
 
+function runInPage(fn, arg)
+{
+  var script = document.createElement("script");
+  script.type = "application/javascript";
+  script.async = false;
+  script.textContent = "(" + fn + ")(" + JSON.stringify(arg) + ");";
+  document.documentElement.appendChild(script);
+  document.documentElement.removeChild(script);
+}
+
 function reinjectStyleSheetWhenRemoved(document, style)
 {
   if (!MutationObserver)
     return null;
 
+  var rules = style.sheet.rules;
   var parentNode = style.parentNode;
   var observer = new MutationObserver(function()
   {
     if (style.parentNode != parentNode)
+    {
       parentNode.appendChild(style);
+
+      if (style.sheet.rules.length == 0)
+      {
+        for (var i = 0; i < rules.length; i++)
+          style.sheet.addRule(rules[i].selectorText, "display: none !important;");
+
+        style.id = id;
+        runInPage(
+          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;
 }
 
-function runInPage(fn, arg)
-{
-  var script = document.createElement("script");
-  script.type = "application/javascript";
-  script.async = false;
-  script.textContent = "(" + fn + ")(" + JSON.stringify(arg) + ");";
-  document.documentElement.appendChild(script);
-  document.documentElement.removeChild(script);
-}
-
 function protectStyleSheet(document, style)
 {
   style.id = id;