Issue 5098 - Expose FilterStorage initialization state

lib/filterStorage.js

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-2017 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
@@ skipping 29 matching lines @@
 let formatVersion = 4;
 
 /**
  * This class reads user's filters from disk, manages them in memory
  * and writes them back.
  * @class
  */
 let FilterStorage = exports.FilterStorage =
 {
   /**
+   * Will be set to true after the initial loadFromDisk() call completes.
+   * @type {boolean}
+   */
+  initialized: false,
+
+  /**
    * Version number of the patterns.ini format used.
    * @type {number}
    */
   get formatVersion()
   {
     return formatVersion;
   },
 
   /**
    * File that the filter list has been loaded from and should be saved to
@@ skipping 396 matching lines @@
    */
   loadFromDisk()
   {
     let readFile = () =>
     {
       let parser = {
         process: this.importData()
       };
       IO.readFromFile(this.sourceFile, parser, readFromFileException =>
       {
+        this.initialized = true;
+
         if (!readFromFileException && this.subscriptions.length == 0)
         {
           // No filter subscriptions in the file, this isn't right.
           readFromFileException = new Error("No data in the file");
         }
 
         if (readFromFileException)
           Cu.reportError(readFromFileException);
 
         if (readFromFileException)
@@ skipping 11 matching lines @@
       {
         // Give up
       });
     };
 
     IO.statFile(this.sourceFile, (statError, statData) =>
     {
       if (statError || !statData.exists)
       {
         this.firstRun = true;
+        this.initialized = true;
         FilterNotifier.triggerListeners("load");
       }
       else
         readFile();
     });
   },
 
   /**
    * Restores an automatically created backup.
    * @param {number} backupIndex
@@ skipping 382 matching lines @@
       Subscription.knownSubscriptions = origKnownSubscriptions;
     }
 
     // Allow events to be processed every now and then.
     // Note: IO.readFromFile() will deal with the potential reentrance here.
     this.linesProcessed++;
     if (this.linesProcessed % 1000 == 0)
       return Utils.yield();
   }
 };