Issue 6999 - Generate style sheets in background page

lib/contentFiltering.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
  * 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/>.
  */
 
 /** @module contentFiltering */
 
 "use strict";
 
 const {RegExpFilter} = require("../adblockpluscore/lib/filterClasses");
-const {ElemHide, createStyleSheet} = require("../adblockpluscore/lib/elemHide");
+const {ElemHide, createStyleSheet,
+       rulesFromStyleSheet} = require("../adblockpluscore/lib/elemHide");
 const {ElemHideEmulation} = require("../adblockpluscore/lib/elemHideEmulation");
 const {filterNotifier} = require("../adblockpluscore/lib/filterNotifier");
 const {Snippets, compileScript} = require("../adblockpluscore/lib/snippets");
 const {checkWhitelisted} = require("./whitelisting");
 const {extractHostFromFrame} = require("./url");
 const {port} = require("./messaging");
 const {HitLogger, logRequest} = require("./hitLogger");
 const info = require("info");
 
 // Chromium's support for tabs.removeCSS is still a work in progress and the
@@ skipping 204 matching lines @@
 
   if (!inline && !updateFrameStyles(sender.page.id, sender.frame.id,
                                     styleSheet.code))
   {
     inline = true;
   }
 
   let response = {trace, inline, emulatedPatterns};
 
   if (inline)
-    response.styleSheet = styleSheet;
-  else if (trace)
-    response.styleSheet = {selectors: styleSheet.selectors};
+    response.rules = [...rulesFromStyleSheet(styleSheet.code)];
+
+  if (trace)
+    response.selectors = styleSheet.selectors;
 
   return response;
 });
 
 port.on("content.injectSelectors", (message, sender) =>
 {
-  updateFrameStyles(sender.page.id, sender.frame.id,
-                    createStyleSheet(message.selectors),
-                    message.groupName, message.appendOnly);
+  let styleSheet = createStyleSheet(message.selectors);
+  if (!userStyleSheetsSupported ||
+      !updateFrameStyles(sender.page.id, sender.frame.id, styleSheet,
+                         message.groupName, message.appendOnly))
+  {
+    return [...rulesFromStyleSheet(styleSheet)];
+  }
 });
 
 fetch(browser.extension.getURL("/snippets.js"), {cache: "no-cache"})
 .then(response => response.ok ? response.text() : "")
 .then(text =>
 {
   snippetsLibrarySource = text;
 });