Issue 4221 - Only forward one elemhideupdate message per update batch to the content process

lib/elemHideFF.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/>.
  */
 
 "use strict";
 
 let {port} = require("messaging");
 let {ElemHide} = require("elemHide");
 let {FilterNotifier} = require("filterNotifier");
 let {FilterStorage} = require("filterStorage");
 let {Prefs} = require("prefs");
 let {Policy} = require("contentPolicy");
+let {Utils} = require("utils");
 
-FilterNotifier.on("elemhideupdate", () => port.emit("elemhideupdate"));
+let isDirty = false;
+FilterNotifier.on("elemhideupdate", () =>
+{
+  // Notify content process asynchronously, only one message per update batch.
+  if (!isDirty)
+  {
+    isDirty = true;
+    Utils.runAsync(() => {
+      isDirty = false;
+      port.emit("elemhideupdate")
+    });
+  }
+});
 
 port.on("getSelectors", () => ElemHide.getSelectors());
 
 port.on("elemhideEnabled", ({frames, isPrivate}) =>
 {
   if (!Prefs.enabled)
     return {enabled: false};
 
   let hit = Policy.isFrameWhitelisted(frames, true);
   if (hit)
   {
     let [frameIndex, contentType, docDomain, thirdParty, location, filter] = hit;
     if (!isPrivate)
       FilterStorage.increaseHitCount(filter);
     return {
       enabled: false,
       contentType, docDomain, thirdParty, location,
       filter: filter.text, filterType: filter.type
     };
   }
   else
     return {enabled: true};
 });